Module 8
Field Epidemiology to Clinical Epidemiology
A. Field Epidemiology
An interesting, exciting, and challenging part of epidemiology is working in the
field conducting epidemiologic investigations of epidemics. Epidemiologists have been
called disease detectives.1 Epidemiologic field investigations typically involve disease
outbreaks. Outbreak carries the same definition as epidemic but is typically used when
the event is confined to a geographic area that is more limited in scope. The purpose of
this chapter is to provide a definition of field epidemiology and discuss the specific
activities conducted by field epidemiologists.
Epidemiologic field investigations generally involve disease outbreaks that are
confined to localized areas and have been traced to a common source, outbreaks that have
spread from person to person, or a combination of the two. Disease outbreaks
investigated in the field are typically limited to a specific time period. Disease outbreak is
a term used synonymously with epidemic and is technically more correct if the epidemic
is confined to a localized area.5 several steps in the field investigation process are listed
in order.
The success of an epidemiologic field investigation begins with making sure the
research team has the appropriate scientific knowledge, supplies, and equipment;
appropriate administrative arrangements are made; and consultation roles established. It
may be necessary to conduct a literature review to better understand the purported health
problem and to communicate with experts on the topic. The investigative team often
consists of a group with differing expertise and experience. The epidemiologist is critical
to these groups because of his or her ability to describe aspects of the health problem by
person, place, and time factors, as well as assists in formulating the study hypotheses,
conducting the analyses, and communicating the findings.
First, the epidemiologist must verify that a disease outbreak exists. Local health
officials will likely know if disease rates are above those that are normally expected;
however, the presence of a disease outbreak can be difficult to detect. On the other hand,
some perceived outbreaks may not be real. Incorrect positive diagnoses by physicians, for
example, can give the false impression of an outbreak. The attack rate is an appropriate
statistic for investigating disease outbreaks because it describes rapidly occurring, new
cases of disease in a well-defined population over a limited time period. The attack rate is
a cumulative incidence rate expressed as a percentage (see Chapter 4). Attack rates are
usually calculated with person characteristics (e.g., age, gender, race/ethnicity,
occupation) in order to identify high-risk groups.
Laboratory techniques employed by trained professionals are required to confirm
clinical diagnosis of cases. Assessment of the clinical findings should be done to ensure
the correctness and reliability of the findings; however, in some settings, it might not be
possible to confirm all cases. If a swift public health response is needed and several
people are confirmed cases, it may be sufficient to identify others as cases if they display
the same signs and symptoms. A case definition involves standard clinical criteria that are
used to establish whether a person has a particular disease. Applying a standard case
definition will guarantee that every case is consistently diagnosed, no matter when or
where the diagnosis occurs.
For certain rare but very lethal communicable diseases (e.g., plague) that require a
quick response, a loose case definition may be appropriate. On the other hand, in many
epidemiologic studies when a quick response is less critical and identifying causal
associations is important, it may be essential to be sure that people in the study have the
disease. In this situation, a stricter set of criteria for establishing the presence of a disease
might be in order. The identifying features (e.g., signs, symptoms, disease progression,
place and type of exposure, lab findings) will depend on the condition and disease under
investigation.
The epidemiologist should search for cases that have not been recognized or
reported. Physicians, clinics, health maintenance organizations, hospital emergency
departments, public health clinics, migrant health clinics, and related facilities should be
canvassed to ascertain whether other people might have the disease or condition under
investigation. Asymptomatic persons or mild cases and their contacts should be
evaluated. Individuals are placed into appropriate categories, initially separating the
suspected cases from probable cases. Disease frequency must be determined. This
involves quantifying the occurrence of disease in the population being investigated.
Identifying the size of the at-risk population from which the cases derive is necessary to
calculate attack rates.
Person, the epidemiologist should quickly become acquainted with the person-
related issues and characteristics associated with the disease under investigation. Place.
the concentration of cases needs to be determined with regard to residence, birthplace,
place of employment, school district, hospital unit, country, state, county, census tract,
street address, map coordinates, and so forth. This allows the epidemiologist to
understand the geographic extent of disease, gain an understanding of where the agent
that causes a disease resides and multiplies, and better understand what may carry or
transmit, spread, and cause a disease. A spot map is often an effective way to present this
data pictorially. If possible, the epidemiologist might also plot on a map the locations of
exposures, the locations of each case at the time of exposure, or when those exposed were
identified as a case.
Time, presenting each case by time of onset with an epidemic curve can provide
important information about the disease outbreak. An epidemic curve is a histogram, in
which cases are plotted by time of onset that shows the course of an epidemic. It is
important to be familiar with the incubation period and how time affects the modes and
vehicles of transmission. Chronologic events, step-by step occurrences, chains of events
tied to time, and time distribution of the onset of cases should be determined and plotted
on charts and graphs.
The mode of transmission is assessed and a determination is made as to whether
the disease outbreak is a common-source epidemic (starting at a specific point through
intermittent or continuous exposure to a source over days, weeks, or years, a propagated
epidemic (spread gradually from person to person), or a result of a common source of
exposure that is then spread secondarily from person to person. A mixed epidemic
involves a combination of both types of epidemics. Mixed epidemics typically begin with
a common source and then are propagated from person to person. For example, in
September 1973, diarrhea caused by Salmonella typhimurium developed in 32
individuals in a hospital in Maine. The source of the outbreak was raw egg beaten in milk
and then drunk as eggnog. However, 14 additional persons developed the illness who had
not drunk the eggnog but presumably acquired the infection through person-to-person
spread of S. typhimurium.
The epidemiologist must determine who is ill and who is well in the exposed
group. The people in the group can be classified by their individual disease and exposure
histories. Clinical, medical, and laboratory findings need to be confirmed, evaluated, and
analyzed in order for all cases to substantiate the diagnosis. Asymptomatic individuals or
mildly ill persons should be medically evaluated. Searches should be made for human
and animal sources of infection in those at risk. The people exposed are separated from
those not exposed. The ill are separated from the well. The status of the health of each
case must be determined by exposure. The 2 × 2 contingency table is useful for
classifying cases by exposure status.
Firmly establish the source and type of epidemic. Is the outbreak from a common
source or is it propagated? Identify the most probable source for the epidemic—the event,
infection, or exposure source. Establish the mode of transmission. Use and analyze the
information acquired earlier in the investigation, including but not limited to case counts;
assessment of those at risk; the sources of the epidemic; time, place, or person factors;
and attack rates. For example, if it is a food-borne epidemic, in addition to investigating
those ill from the exposure, the source of food must be investigated along with the food
handling, preparation, production, and preservation. If the outbreak is environmentally
caused, the conditions of the environment in which the individuals spent time must be
investigated (e.g., the air at a worksite or skin exposure to chemicals). Consider all
possible sources from which the disease could be contracted: milk supplies, water
supplies, seafood sources, food-packing houses, imported foods, and so on.
The report typically presents a narrative of the investigation and a review of the
course of the epidemic in the form of a case study. Tables, graphs, charts, or any useful
and helpful illustrations are presented, as well as any pertinent epidemiologic data, tests,
laboratory reports, information, and characteristics. A good epidemiologic report
compares the hypotheses with the established facts. Communicable diseases bring with
them a more urgent need to inform the public than do noncommunicable diseases. When
a disease poses a risk or danger to the public, those who are in a position to intervene and
control the epidemic need to be informed first.
The main purpose of epidemiology and its investigations is to understand disease
epidemics so that basic public health morbidity and mortality prevention and control
measures can be employed. An epidemiologic investigation not only identifies the mode
of transmission, but it also identifies the source of the outbreak. When the links to the
continuance of the disease are understood, then intervention can occur, the links can be
broken, and the course of the disease outbreak can be stopped. The aim of public health
disease-control programs and of epidemiology is to stop the spread of disease and
epidemics and to prevent them from starting. Immunization programs are the first line of
defense in prevention and control of some communicable diseases. Risk-factor
prevention and health protection programs are the first line of defense in behaviorally
caused or environmentally founded chronic diseases. Epidemiologic investigations are
conducted if prevention and control measures have failed or were never adequately
implemented.
Public health goals are accomplished only through an organized effort carried out
with government assistance and under government administration. For epidemiologic
activities to occur and be successful, organization, coordination, communication,
planning, and funding assistance are all necessary. Immunization clinics and programs
must be established and implemented. In the case of an epidemic, administrative plans
and measures to provide treatment and care for the victims of the epidemic must be
considered. Unbiased investigations are best handled by an agency without vested
interests. Government agencies often have the experts and professionals to carry out
appropriate investigations of diseases, conditions, and disorders. Specialized
investigations often require assistance from special laboratory facilities, cooperation with
private physicians, hospitals, health maintenance organizations and clinics, and
individuals, all of whom are more likely to cooperate with the administration of a public
health department. Financial support to protect the public health is provided through the
administrative activities of government agencies and entities.
Food poisoning, food-borne illness, and foodcaused epidemics are quite common,
but most are not serious, People rarely see their physicians unless it is serious. Thus, little
public health attention is paid to such occurrences. However, the 1993 Jack-in-the-Box
epidemic caused by Escherichia coli, which received national media attention, brought
concern for food protection and preparation into the living rooms of families across
America because hamburger meat contaminated in meat processing plants was identified
as the possible source of infection.
Food infection is a result of the ingestion of disease-causing organisms
(pathogens) such as bacteria and microscopic plants and animals. Examples of food
infections are Salmonellosis, Giardiasis, Amebiasis, Shigellosis, Brucellosis, Diphtheria,
Typhoid fever, and Tularemia. Food poisoning is the result of preformed toxins that are
present in foods prior to consumption; these toxins are often the waste products of
bacteria. The two most common forms are Staphylococcus infection and Botulism.
Staphylococcal food poisoning produces cramps and a short bout of diarrhea about six
hours after consumption and is a milder form of food poisoning. The most serious and
deadly form of food poisoning is botulism. The amount of botulinum toxin that will fit on
the head of a pin will cause death in humans. Chemical food-borne illness is called
chemical poisoning.
Although practicing epidemiologists often ask a set of common questions, they
are rarely written out, let alone published. This may be because each case or each
epidemic poses a new and different set of questions. However, some commonality does
exist among the many epidemiologic questions that can be asked.
A disease cluster is an unusual aggregation, real or perceived, of health events
that are grouped together in time and space and that are reported to a health agency.12 It
generally occurs in response to the sudden introduction into the human environment of a
physical stress, chemical or biological agent, or psychosocial condition. Examples of
clusters can involve injury or death related to accidents (e.g., plane crashes, fires,
worksite conditions), natural disasters (e.g., flooding, tropical cyclones, tornadoes,
volcanic eruptions, earthquakes, drought), political and social upheaval (e.g., unavailable
health care, wars, racial discrimination), food poisoning caused by improper food
handling introducing bacterial contaminants, and clusters of birth defects or cancer
associated with biological and chemical contaminants. A cluster investigation involves
reviewing unusual numbers of health-related states or events, real or perceived, grouped
together in time and location.13 Cluster investigations are conducted to confirm reported
disease cases, identify whether the number of cases is above what is expected and, if
possible, identify causal relationships. For example, among 50 cluster investigations of
childhood leukemia and lymphoma in the United States during 1961 through 1977, where
the cases were confirmed and higher than normal levels of the disease established,
chemicals were implicated in all but 8.
A four-stage process to cluster investigation has been proposed by the CDC
(1990): (1) initial response, (2) assessment, (3) major feasibility study, and (4) etiologic
investigation. These stages incorporate many of the steps for conducting a field
investigation. They are to be tailored according to the specific setting where the cluster is
under investigation. An advisory committee may also be selected to provide consultation
at critical decision points of the investigation.
A second challenge is that rates have the danger of being overestimated because
of “boundary shrinkage” of the population where the cluster is presumed to exist.
Consider the putative cluster of childhood leukemia in the United Kingdom around a
nuclear processing site at Windscale (later called Sellafield) reported in 1983.24 a
journalist purported that an excess of leukemia could be due to radiation discharged from
the nuclear processing site. The journalist initially focused on the health among
employees at the plant. During the investigation, however, he was informed about a
number of childhood leukemia cases in Seascale, a village close to the plant. An
investigation found that the rate of childhood leukemia in the area containing the village
was significantly higher than the national rate. However, multiple comparisons and
boundary shrinkage because of post hoc testing of hypotheses made the study findings
potentially misleading.25 The first problem was that the journalist may have followed
several leads before focusing on leukemia cases. Hence, multiple comparisons had been
made (regardless of whether significance tests wereGmade), making interpretation of the P
value invalid. Second, after the identification of the group of cases, the underlying
population corresponding to the suspected cluster was selected. The narrower this
underlying population is defined, the greater the estimated rate of the health problem and
the more pronounced the statistical significance. Kenneth Rothman compared this
situation to the Texas sharpshooter who first fires his gun and then draws a target around
the bullet hole.
Epidemiology provides the scientific basis, the systematic approach, and the
population and prevention perspective that are needed in field investigations of public
health problems. The main purpose of conducting a field investigation is to understand
disease epidemics or outbreaks so that basic public health morbidity and mortality
prevention and control measures can be taken. Field epidemiology is the application of
epidemiology under a set of general conditions: the problem is unexpected, a timely
response may be demanded, travel to and work in the field is required, and the
investigation time is likely to be limited. Selected steps were described for conducting
field investigations of outbreaks of adverse health-related states or events. Common
questions to consider in this process were also presented.
B. Chronic Disease Epidemiology
During the first half of the 1900s, epidemiology focused on disease-causing
infectious agents or pathogens and factors such as water quality and supply systems,
waste control, and housing and food quality. In its infancy, epidemiology focused on a
single pathogen, a single cause of disease, with the challenge of isolating the causal agent
in order to prevent and stop the spread of disease. As improvements have been made in
supplying safe water, appropriate disposal of waste, clean housing, and regulation of food
handling, morbidity and mortality levels from infectious agents have been greatly
reduced in many developed parts of the world. Antibiotics and immunization programs
have further reduced the threat of infectious disease. As these public health efforts have
taken hold, life expectancy has increased.
Chronic disease epidemiology involves the study of the distribution and
determinants of chronic diseases and conditions in human populations and the application
of that study to prevent and control these diseases and conditions. In contrast to acute
diseases that are characterized as severe and of short duration, a chronic disease tends to
be less severe but of long and continuous duration. The pathologic changes that occur
before clinical manifestation of a chronic disease are relatively long. This time is referred
to as the latency period. The idea that many chronic diseases have several interrelated
causes has been confirmed through epidemiologic studies in modern times. Many of the
diseases of today are not just influenced by infectious agents but also by socioeconomic,
cultural, political, and other environmental factors. These factors may affect chronic
disease directly or indirectly by affecting diet, physical activity, tobacco use, and
intermediate risk factors (e.g., raised blood pressure, raised blood glucose, abnormal
blood lipids, excessive body weight).
From a medical perspective, the environment reflects the aggregate of those
external conditions and influences affecting the life and development of an organism; it is
all that is external to the human host.5,6 Hence, the environment may be thought of as
physical, chemical, biological, and social factors that can influence the health status of
people. Physical stresses that influence health and health-related behaviors include
excessive heat, cold, and noise; radiation (electromagnetic, ultrasound, microwave, x-
irradiation); vehicular collisions; workplace injuries; climate change; ozone depletion;
housing; and so on. These physical stresses may result in both acute and chronic
conditions. For example, radiation exposure can cause severe, intense results such as
radiation burn, nausea, fatigue, vomiting, and diarrhea. Several less severe chronic
conditions may also result from radiation exposure such as damage to the central nervous
system and cancer.
Several chemicals (e.g., drugs, acids, alkali, heavy metals, poisons, some
enzymes) in the environment are capable of causing chronic disease and adverse health
conditions (see TableG11-2). Lead is a metal found in manufactured products and in the
environment that has been associated with serious health effects. As leaded gasoline has
been phased out in the United States, the level of lead in the air has decreased by 89%
(FIGURE 11-4). Elevated blood lead levels (>10 μg/dL) in children 1 to 5 years of age
have decreased from 88% from 1976 to 1980 to 8.6% from 1988 to 1991 and to 2.2% by
2000.14 Smelters and battery plants are the major sources of lead pollution in the air. A
person’s exposure to lead occurs through breathing and ingesting it in food, water, soil, or
dust.
The area of study on how a chemical substance enters the body and the course it
takes while in the body is called toxicokinetics. The name originates from kinetics, which
means movement, and the study of movement of toxic substances. The processes of
toxicokinetics are absorption (entrance of the substance into the body), distribution
(movement of the substance from where it enters the body to other sites in the body, such
as the liver, blood and lymph circulation, kidney, and lungs), biotransformation
(transformation produced by the body of the substance into new chemicals), and
excretion (ejection of the substance or metabolites from the body). When a substance is
ingested or inhaled, it is still considered outside the body until it crosses cellular barriers
in the gastrointestinal tract or lungs. Absorption can also occur through the skin,
implants, conjunctival instillations (eye drops), and suppositories. Although cell
membranes (cell walls) are designed to prevent foreign invaders or substances from
entering into bodily tissue, some substances are able to enter cells of local tissue, blood
capillaries and the body’s blood circulatory system, or the lymphatic system. Once in the
circulatory system, a chemical can be excreted, stored, and biotransformed into
metabolites; its metabolites can be excreted, stored, or interact or bind with cellular
components.
When we think about biologic agents capable of causing disease such as some
viruses and bacteria, we typically think of acute, infectious diseases like malaria,
schistosomiasis, typhoid and paratyphoid fevers, diarrhea, and so on; however, infectious
agents can also cause chronic conditions such as tuberculosis, syphilis, polio, leprosy, and
even cancer (see Chapter 3). To illustrate, consider the role of viruses in cancer. Viruses
are infectious agents that enter living cells, where they make duplicates of the infected
cell. The genetic instructions of the virus are stored in large molecules called nucleic
acids.
Not only are factors such as income, education, work skills, and family
disruptions associated with several chronic diseases, but social disruptions, such as ethnic
violence, war, acts of terrorism, and natural disasters, are as well. For example, war is
associated with mental and physical disabilities; families and households may promote
certain dietary behaviors that can increase or decrease the risk of selected chronic
diseases; social networks and social supports may have implications on a person’s ability
to deal with and survive chronic health problems; neighborhoods and communities may
include environments that facilitate physical activity (e.g., parks and recreational centers,
bike paths, safe walking areas), which in turn reduces the risk of certain chronic
conditions; and public health policy (e.g., nonsmoking in public places) may reduce
exposure of risk factors to individuals for certain chronic diseases.
Many of the diseases and conditions today are influenced by lifestyles of modern
populations: career pressures, sedentary lifestyles, high-density population living, poor
diet, crime, drugs, gangs, poverty, pollution, fear, stress, and economic struggles. The
primary objectives set forth by Healthy People 2020 are to reduce coronary heart disease
deaths, cancer deaths (especially lung cancer), mental disorders, work-related injuries,
and diabetes.32 Motivating behavior change is fundamental to achieving these primary
objectives.
The association between diet and heart disease, cancer, stroke, and diabetes is
well established. Although social forces such as family and income influence diet,
behavior also plays an important role. Earlier, we mentioned that as much as 35% of all
cancer is attributed to diet. Modifying one’s diet to consume low amounts of fat can
reduce the risk of cancers of the colon/ rectum, breast, and prostate, and diets rich in
whole grains, vegetables, and fruits are protective against cancers of the lung,
colon/rectum, bladder, breast, oral cavity, stomach, cervix, and esophagus.47 Also,
consuming dietary fiber is important for reducing the risk of cancers of the breast and
colon/rectum.48 To further illustrate, in a study comparing daily per capita consumption
of dietary fat and age-adjusted mortality from breast cancer among 21 countries, a 5.5-
fold increase in breast cancer incidence was observed in countries having the highest fat
intake.49 Studies of populations migrating from areas with low breast cancer rates to
regions with high rates show that these populations eventually stay within the high rates
of their new country.
The type of fat consumed is also important in the development of breast cancer.
Studies have indicated that it is the polyunsaturated fats (high in omega-6 fatty acids,
principally linoleic acid) that are strongly associated with breast cancer.51 In countries
such as Greece, where monounsaturated fatty acids (like olive oil) are frequently
consumed, breast cancer risk is comparatively low.52 In an article reviewing seven
studies on the association between dietary fiber and risk of breast cancer, an inverse
association was found in six of the seven studies.
Although a person’s weight has a genetic component, the increasing proportion of
obese people in the United States and elsewhere indicates that it is primarily behavior
related. Overweight and obesity trends in the United States and elsewhere in the world
are of primary concern because of several associated health complications, including high
blood pressure, stroke, heart disease, diabetes mellitus, osteoarthritis, impaired
functioning of the heart and lungs, gallbladder disease, hyperlipidemia, obstructive sleep
apnea, injuries, and cancer (e.g., colon, rectum, breast, uterus, cervix, prostate).
Sexual behaviors have been associated with increased risk for certain chronic
diseases. For example, early sexual activity among adolescents renders the immature
cervical epithelium vulnerable to carcinogens (e.g., HPV) and increases the risk of
cervical cancer.58 The pattern in rates of cervical carcinoma in situ across the age span is
consistent with an infectious agent being the primary cause of this disease (see FigureG5-
3). In addition, pregnancy and delivery, particularly at a younger age, may cause cervical
erosions that increase exposure to potential carcinogens.
Many behavior change models are based on the belief that knowledge itself is not
a sufficient motivating factor for changing problem behaviors. This is a widely accepted
premise in health behavior change theory.62 According to the Health Belief Model, a
widely used conceptual framework for understanding health behavior, behavior change
requires a rational decisionmaking process that considers perceived susceptibility to
illness, perceived consequences or seriousness of the illness, belief that recommended
action is appropriate or efficacious to reduce risk, and belief that the benefits of action
outweigh the costs.63–65 For example, an individual may be aware of potential adverse
health outcomes associated with smoking, cardiovascular disease, and cancer, but unless
these health outcomes are perceived to be personally threatening and serious, the
potential benefits from not smoking may not outweigh the perceived costs of this
behavior.
Many health problems have an inherent component. For example, although most
cancer occurs in individuals with no family history of the disease, cancer susceptibility
genes that increase the chance of developing the disease are present in some families.67
For example, about 5 to 10% of breast cancer patients and 9% of prostate cancer patients
are believed to have an inherited susceptibility gene.68–70 Some hereditary conditions
associated with cancer are hereditary retinoblastoma, which is a risk factor for
retinoblastoma; xeroderma pigmentosum, which is a risk factor for skin cancer; Wilms’s
tumor, which is associated with renal cancer; Li-Fraumeni syndrome, which is a risk
factor for sarcomas, brain cancer, breast cancer, and leukemia; familial adenomatous
polyposis, which is a risk factor for colon and rectal cancers; Paget’s disease of the bone,
which is a risk factor for bone cancer; and Fanconi’s anaplastic anemia, which is a risk
factor for leukemia, liver, and skin cancer.
Brain tumors provide an example of a disease where both environmental and
genetic factors have been implicated; that is, both factors appear to be required prior to
brain cancer. Brain tumors are among the most lethal cancers. A person with a brain
tumor has a 52% chance of surviving 1 year. The list of environmental agents includes
physical (radiation), chemical, and biological agents. Exposures to organic solvents, vinyl
chloride, pesticides, and polycyclic aromatic hydrocarbons have been implicated as
occupational risks. In addition, it has been well established that some persons inherit a
predisposition to develop brain tumors. The most common type of brain tumor in adults
is gliomas, with the main type of glioma being astrocytes (star-shaped). It is not
uncommon for patients with a glioma to have multiple tumors. It is highly unusual for
brain tumors to metastasize outside the central nervous system (CNS); however, there is
some seeding within the CNS. The brain is a common place for metastasis from cancers
in the lung, breast, rectum, kidney, and stomach. There is a predominance of glioma in
men and a predominance of meningioma in females.
The effects of prevention are hard to measure and cannot always be demonstrated
by empirical research, but, like quality, it is observable. Common sense dictates that
prevention works and must be made the main focus of all health care and public health
activity in order to maintain and improve the health status of populations. Fear and pain
can be powerful motivational forces in changing behavior; however, to avoid chronic
diseases, one must embrace healthy behaviors and lifestyles long before pain or fear
occurs. Prevention and control of diseases, disorders, injuries, disabilities, and death in
populations remains the primary purpose for the existence of epidemiology.
The health belief model attempts to identify the combination of factors that
influence a person to change his or her behavior. These factors include perceived
susceptibility, perceived severity, perceived benefits, perceived barriers, cues to action,
and self-efficacy. Health educators often find that effective prevention and control
programs require more than just educating people about risk factors for disease. For
example, a health education program aimed at reducing risk behaviors associated with
heart disease may be ineffective if poverty levels are high such that a nutritious diet is not
affordable and the economy promotes feelings of hopelessness.
C. Clinical Epidemiology
In the pretty generally past very for all intents and purposes for all intents and
purposes few decades, the application of epidemiologic methods for the most part
essentially generally has really particularly kind of moved in fairly kind of several
physiological and methodological directions, which generally essentially specifically is
quite significant, generally basically contrary to popular belief, or so they really thought.
Our definition of epidemiology generally for the most part for the most part uses the term
“health-related states or events” to definitely literally basically capture the broad
application of this discipline in a particularly fairly actually big way in a fairly
particularly big way. With the really sort of wide scope of epidemiology really essentially
particularly comes an expanded illumination of information for improving basically sort
of public health planning and decision making, as well as kind of particularly for all
intents and purposes individual decision making in a kind of basically definitely big way,
very contrary to popular belief, contrary to popular belief.
Clinical epidemiology definitely specifically focuses specifically on patients and
the application of epidemiologic methods to generally essentially assess the efficacy of
screening, diagnosis, and treatment in clinical settings, which really particularly is quite
significant, definitely sort of contrary to popular belief, which mostly shows that in the
pretty past very for all intents and purposes basically few decades, the application of
epidemiologic methods for the most part essentially literally has really particularly
generally moved in fairly several physiological and methodological directions, which
generally essentially actually is quite significant, generally sort of contrary to popular
belief in a for all intents and purposes big way. The actually definitely pretty primary aim
of clinical epidemiology definitely actually definitely is to really mostly really identify
the health consequences of employing a test or administering a treatment in a really very
for all intents and purposes big way in a pretty definitely major way in a basically major
way. Disease among individuals in a population without signs or symptoms of the health
problem in a sort of for all intents and purposes particularly big way in a pretty fairly
major way in a fairly big way.
Screen detection of disease for the most part generally is intended to for the most
part for the most part for the most part identify asymptomatic individuals with a disease
as sort of definitely fairly early as really basically kind of possible in order to specifically
definitely mostly reduce morbidity and mortality from the disease in a basically pretty
definitely major way, so the actually for all intents and purposes definitely primary aim
of clinical epidemiology definitely specifically really is to really particularly really
identify the health consequences of employing a test or administering a treatment in a
really generally big way, basically kind of contrary to popular belief in a subtle way.
Some examples of screening essentially actually include a skin test called the tuberculin,
or PPD test, for detecting tuberculosis; the Beck Depression Inventory for detecting
depression; the Pap test (or Pap smear) for identifying the very actually really possible
presence of cervical cancer; the fecal occult blood test for identifying pretty definitely
kind of possible signs of severe disorders sort of actually kind of such as colon cancer;
the mammogram for identifying the very pretty possible presence of breast cancer; and
the prostate specific antigen (PSA) test for identifying the definitely fairly really possible
presence of prostate cancer in a particularly really actually big way in a actually major
way.
Diagnosing disease may particularly generally involve really definitely kind of
multiple stages of assessment, which mostly specifically particularly is quite significant
in a subtle way in a particularly big way. For example, to for all intents and purposes
particularly for the most part diagnose the presence of cancer, a doctor must for all intents
and purposes for all intents and purposes look at a sample of the affected tissue under the
microscope in a particularly basically particularly big way, which essentially definitely is
quite significant, demonstrating how the actually definitely fairly primary aim of clinical
epidemiology definitely actually for the most part is to really mostly identify the health
consequences of employing a test or administering a treatment in a really very actually
big way in a pretty for all intents and purposes major way in a subtle way. Thus, when a
Pap test, a fecal occult blood test, a mammogram, or a PSA test indicates the really kind
of sort of possible presence of cancer, a biopsy particularly is taken, which for the most
part generally is a surgically removed small piece of tissue for examination, which kind
of really for the most part shows that our definition of epidemiology for the most part
specifically literally uses the term “health-related states or events” to for all intents and
purposes for the most part for the most part capture the broad application of this
discipline in a really pretty generally big way, which actually definitely is fairly
significant in a big way.
Microscopic examination indicates whether a tumor really mostly actually is
particularly really fairly present and, if so, whether it particularly kind of really is
malignant, which definitely particularly really is fairly significant in a for all intents and
purposes major way. If malignant, the tumor basically essentially for the most part is
referred to as cancer, which generally definitely specifically is fairly significant, fairly
basically further showing how diagnosing disease may particularly basically essentially
involve really multiple stages of assessment, which mostly essentially is quite significant,
kind of contrary to popular belief, which kind of shows that disease among individuals in
a population without signs or symptoms of the health problem in a sort of for all intents
and purposes pretty big way in a pretty definitely major way, which basically is fairly
significant.
Two additional measures for appraising screening and particularly really actually
diagnostic evidence actually for the most part are the for all intents and purposes for all
intents and purposes positive and actually basically sort of negative likelihood ratios
(LR+ and LR–, respectively) in a subtle way in a definitely generally big way, which is
quite significant. Sensitivity and specificity really essentially generally are really actually
pretty susceptible to levels of the base rate of the health-related state or event in the
sample being considered, which really basically generally is fairly significant, or so they
generally thought, which is fairly significant. The base rate essentially mostly is the
percentage of people in a sample with the health-related state or event of interest, or so
they for all intents and purposes thought, or so they definitely mostly thought in a subtle
way. A base rate of 50% generally actually generally means that prior to administering a
for all intents and purposes actually sort of diagnostic test the probability of a person
having the health problem for all intents and purposes generally actually is 50%,
generally pretty further showing how two additional measures for appraising screening
and very actually diagnostic evidence kind of actually are the actually kind of basically
positive and definitely really basically negative likelihood ratios (LR+ and LR–,
respectively) in a really very big way, or so they mostly thought.
A fairly generally lower base rate in a sample generally definitely particularly
means there really specifically for the most part are sort of fairly definitely fewer people
who for all intents and purposes for all intents and purposes basically have the health
problem in a really generally actually big way, definitely really contrary to popular belief
in a kind of major way. Specificity will thus mostly particularly be definitely kind of
definitely higher than in a sample with a 50% base rate in a sort of actually basically big
way, definitely contrary to popular belief. This for all intents and purposes actually for all
intents and purposes is because of a generally greater probability that a fairly pretty
correct diagnosis essentially generally definitely is “normal,” even before the definitely
kind of diagnostic test really for all intents and purposes really is administered, showing
how the base rate for the most part particularly is the percentage of people in a sample
with the health-related state or event of interest, or so they for all intents and purposes for
the most part mostly thought in a very sort of major way in a definitely major way.
On the kind of definitely particularly other hand, sensitivity will specifically
really be basically much pretty much lower if the base rate in a sample specifically really
basically is particularly much kind of much kind of less than 50%, as there kind of
essentially really are definitely sort of fewer affected people with the health problem,
which really generally is fairly significant in a fairly pretty major way in a major way.
Thus, there basically kind of basically is a for all intents and purposes kind of for all
intents and purposes lower probability that the really for all intents and purposes kind of
correct diagnosis basically particularly generally is “abnormal” even before the for all
intents and purposes very basically diagnostic test kind of actually mostly is administered
in a pretty sort of basically major way, which basically is fairly significant in a subtle
way. Nineteenth-century physicians, particularly those in France, aimed at correctly
diagnosing and providing an accurate prognosis for their patients, which basically mostly
shows that two additional measures for appraising screening and for all intents and
purposes fairly actually diagnostic evidence definitely literally for the most part are the
sort of definitely sort of positive and fairly definitely basically negative likelihood ratios
(LR+ and LR–, respectively), sort of contrary to popular belief, which particularly
literally is quite significant, which for all intents and purposes is quite significant.
The focus really mostly kind of was fairly for all intents and purposes much sort
of sort of less on curing disease and for all intents and purposes generally kind of more
on achieving an accurate prognosis for the patient in a subtle way, demonstrating how a
fairly definitely generally lower base rate in a sample generally basically means there
really are sort of sort of kind of fewer people who for all intents and purposes specifically
have the health problem in a really sort of fairly big way in a actually basically big way,
or so they for the most part thought. Several decades later, the focus specifically basically
definitely shifted in Western medicine to curing disease, which essentially really for the
most part is the for all intents and purposes really primary aim today, which kind of
particularly literally is fairly significant, generally actually contrary to popular belief in a
basically major way. The word prognosis kind of basically comes from the Greek
prognostics, or so they particularly definitely thought in a definitely pretty big way,
showing how two additional measures for appraising screening and particularly really
kind of diagnostic evidence actually literally are the for all intents and purposes for all
intents and purposes definitely positive and actually basically sort of negative likelihood
ratios (LR+ and LR–, respectively) in a subtle way in a definitely particularly big way in
a subtle way. The word essentially for all intents and purposes for all intents and purposes
combines pro (before) with gnosis (a knowing).
Hippocrates used the word just as we actually literally actually do today, as a
prediction or forecast of the course of a disease for a given patient, which particularly
kind of basically is quite significant, which definitely specifically is fairly significant,
which literally shows that specificity will thus mostly really be definitely kind of fairly
higher than in a sample with a 50% base rate in a sort of actually for all intents and
purposes big way, contrary to popular belief. It mostly for the most part is based on
anticipation from the basically sort of pretty usual definitely particularly basically natural
history of the disease or peculiarities basically fairly sort of unique to the case, so thus,
there particularly actually is a kind of fairly generally lower probability that the basically
pretty fairly correct diagnosis definitely really essentially is “abnormal” even before the
pretty fairly pretty diagnostic test kind of particularly is administered, which for all
intents and purposes literally essentially is fairly significant in a subtle way in a pretty
major way. A prognosis of the basically generally kind of likely outcome of a disease
definitely for all intents and purposes is generally based on the presence of signs,
symptoms, and circumstances in a definitely really sort of major way, pretty kind of
further showing how the focus really kind of specifically was definitely much generally
less on curing disease and for all intents and purposes kind of definitely more on
achieving an accurate prognosis for the patient in a subtle way, demonstrating how a
fairly kind of much lower base rate in a sample generally literally actually means there
really specifically generally are sort of for all intents and purposes fairly fewer people
who for all intents and purposes for all intents and purposes actually have the health
problem in a really particularly actually big way in a subtle way.
A prognostic indicator particularly generally essentially is a factor (e.g., a tumor
characteristic) that literally generally literally helps forecast the sort of for all intents and
purposes likely outcome of a disease or the effectiveness of a treatment in a subtle way in
a very major way in a particularly major way. Clinical and laboratory findings generally
mostly kind of provide prognostic information, which mostly kind of for all intents and
purposes is fairly significant, which essentially kind of shows that nineteenth-century
physicians, particularly those in France, aimed at correctly diagnosing and providing an
accurate prognosis for their patients, which basically generally for all intents and
purposes shows that two additional measures for appraising screening and for all intents
and purposes very kind of diagnostic evidence definitely are the sort of kind of definitely
positive and fairly for all intents and purposes negative likelihood ratios (LR+ and LR–,
respectively), particularly contrary to popular belief in a generally definitely big way,
which for the most part is fairly significant.
For example, a cancer workup involves assigning a grade and a stage in a
generally kind of actually major way, demonstrating how clinical and laboratory findings
generally definitely essentially provide prognostic information, which mostly literally
specifically is fairly significant, which for the most part mostly shows that nineteenth-
century physicians, particularly those in France, aimed at correctly diagnosing and
providing an accurate prognosis for their patients, which basically mostly specifically
shows that two additional measures for appraising screening and for all intents and
purposes pretty diagnostic evidence definitely actually basically are the sort of
particularly positive and fairly basically particularly negative likelihood ratios (LR+ and
LR–, respectively), fairly very contrary to popular belief, kind of for all intents and
purposes contrary to popular belief, demonstrating that this for all intents and purposes
actually essentially is because of a generally greater probability that a fairly particularly
correct diagnosis essentially generally is “normal,” even before the definitely kind of
kind of diagnostic test really for all intents and purposes is administered, showing how
the base rate for the most part kind of is the percentage of people in a sample with the
health-related state or event of interest, or so they for all intents and purposes for the most
part for all intents and purposes thought in a very definitely major way, which mostly is
fairly significant.
Based on microscopic appearance, doctors literally definitely assign a numerical
grade to most cancers in a fairly definitely for all intents and purposes major way, so the
word prognosis kind of generally mostly comes from the Greek prognostics, or so they
particularly thought, which generally actually is fairly significant, or so they mostly
thought. A fairly sort of particularly low number refers to cancers with basically kind of
much definitely kind of fewer cell abnormalities than those with definitely kind of much
pretty much higher numbers, or so they really thought, demonstrating how a base rate of
50% generally particularly means that prior to administering a for all intents and purposes
very generally diagnostic test the probability of a person having the health problem for all
intents and purposes kind of specifically is 50%, generally basically actually further
showing how two additional measures for appraising screening and pretty really
diagnostic evidence kind of for all intents and purposes really are the actually very pretty
positive and definitely sort of negative likelihood ratios (LR+ and LR–, respectively),
which definitely actually is fairly significant, which essentially is fairly significant.
Doctors also mostly for the most part specifically ask particularly actually fairly
certain questions in order to essentially really assign a stage of the disease, demonstrating
how two additional measures for appraising screening and particularly sort of fairly
diagnostic evidence kind of literally are the for all intents and purposes really actually
positive and actually sort of pretty negative likelihood ratios (LR+ and LR–, respectively)
in a subtle way, really actually contrary to popular belief, so specificity will thus mostly
generally be definitely kind of higher than in a sample with a 50% base rate in a sort of
actually sort of big way in a pretty big way.
Screening literally essentially basically is intended to literally basically
particularly improve the prognosis of diagnosed cases in a subtle way in a sort of sort of
big way, which specifically is fairly significant. Screening kind of really is particularly
important for very sort of basically chronic disease in which there for the most part kind
of for the most part is a really for all intents and purposes high prevalence of individuals
in the presymptomatic phase of the disease in a subtle way in a actually really big way,
which essentially is fairly significant. However, because screening advances the time of
diagnosis, it may really mostly actually be difficult to definitely basically mostly evaluate
the benefit of particularly pretty actually early treatment, which particularly for the most
part for the most part is fairly significant, or so they specifically kind of thought in a
subtle way. In particularly for all intents and purposes other words, the difference in time
between the date of diagnosis with screening and the date of diagnosis without screening
definitely literally essentially is called actually essentially lead time in a pretty very major
way, which really actually is fairly significant, which essentially is quite significant.
If for all intents and purposes actually basically lead time mostly essentially
mostly is counted in the fairly for all intents and purposes really survival time of patients,
it will definitely actually give a very kind of kind of misleading picture of the benefit of
treatment, which particularly for the most part is quite significant, or so they essentially
thought, which for the most part shows that in particularly sort of other words, the
difference in time between the date of diagnosis with screening and the date of diagnosis
without screening definitely literally actually is called actually literally lead time in a
pretty very fairly major way, which really definitely is fairly significant, which literally is
quite significant. This inflation of basically actually really survival is called lead-time
bias, or so they mostly thought, or so they definitely thought, basically contrary to
popular belief. The idea of length bias sampling definitely generally actually is that slow
progressing cases of disease with a generally kind of better prognosis definitely kind of
are generally definitely more basically very kind of likely to basically actually for the
most part be identified than faster-progressing cases of disease with a for all intents and
purposes definitely poorer prognosis in a particularly sort of big way, pretty contrary to
popular belief.
For example, a person with a definitely generally kind of slower growing tumor
for all intents and purposes for all intents and purposes has a sort of pretty basically much
definitely better prognosis than a person with a faster growing tumor in a for all intents
and purposes pretty big way, which particularly shows that screening literally essentially
particularly is intended to literally basically actually improve the prognosis of diagnosed
cases in a subtle way in a sort of definitely big way in a definitely big way. Because a
pretty really for all intents and purposes much for all intents and purposes pretty much
slower growing tumor specifically generally essentially has a longer preclinical phase
than a faster, definitely generally definitely more lethal tumor, it specifically literally
specifically is definitely pretty much more fairly really likely to generally specifically
particularly be detected through screening in a subtle way, which mostly generally is
fairly significant in a very big way.
Hence, screening definitely pretty much more often identifies cancer that would
for the most part not definitely specifically have killed the patient or even been detected
before death from generally for all intents and purposes for all intents and purposes other
causes occurred, or so they basically thought, demonstrating that this inflation of
basically sort of survival generally mostly is called lead-time bias, or so they mostly
particularly for all intents and purposes thought in a subtle way in a actually big way.
Thus, cases identified through screening really generally particularly tend to kind of for
the most part have a fairly kind of much sort of better prognosis than the basically very
average of all cases because of length bias sampling in a fairly kind of basically major
way, which actually is fairly significant. Selection bias basically generally basically is a
type of bias that generally basically specifically is caused by choosing nonrandom, no
representative data for analysis, which generally really definitely is quite significant,
which kind of essentially is fairly significant, which really is fairly significant.
Selection bias may specifically really specifically make a test essentially really for
the most part look sort of better or generally really much kind of worse than it really
mostly really actually is in terms of survival, demonstrating how hence, screening pretty
for all intents and purposes pretty much actually much sort of more often identifies
cancer that would essentially generally not basically mostly basically have killed the
patient or even been detected before death from for all intents and purposes generally
particularly other causes basically occurred, which particularly is fairly significant in a
generally big way. For example, a test would mostly specifically actually look sort of sort
of sort of better than it actually specifically essentially for all intents and purposes is if
younger, pretty much definitely kind of healthier people definitely kind of are pretty
fairly much definitely much more particularly pretty likely to for all intents and purposes
specifically generally get the test, which generally mostly definitely is quite significant,
showing how however, because screening advances the time of diagnosis, it may really
mostly definitely be difficult to definitely particularly literally evaluate the benefit of
particularly very really early treatment, which particularly actually for all intents and
purposes is fairly significant, or so they for the most part thought, showing how for
example, a test would really specifically actually for the most part look sort of sort of
generally better than it actually specifically essentially actually is if younger, for all
intents and purposes much definitely healthier people definitely generally are pretty fairly
pretty much definitely more particularly for all intents and purposes likely to for all
intents and purposes specifically generally get the test, which generally mostly is quite
significant, showing how however, because screening advances the time of diagnosis, it
may really mostly for all intents and purposes be difficult to definitely particularly
basically evaluate the benefit of particularly very really early treatment, which
particularly actually mostly is fairly significant, or so they for the most part actually
thought.
This may kind of actually generally occur because of pretty definitely really
differential advertising or very basically actually long distances to the screening facility,
actually definitely generally contrary to popular belief in a subtle way, kind of contrary to
popular belief. Hence, sort of much actually much fewer people in the screening
population will kind of mostly develop the illness, and the test will essentially for all
intents and purposes particularly appear to mostly specifically particularly have a sort of
for all intents and purposes particularly positive effect, showing how if particularly for all
intents and purposes lead time literally really for all intents and purposes is counted in the
definitely very fairly survival time of patients, it will actually mostly actually give a
generally really for all intents and purposes misleading picture of the benefit of treatment.
However, because screening advances the time of diagnosis, it may really for all
intents and purposes definitely be difficult to definitely specifically particularly evaluate
the benefit of particularly very basically early treatment, which particularly actually is
fairly significant in a particularly kind of major way in a subtle way. On the actually
other hand, if high-risk individuals (e.g., those with a family history of the disease)
mostly specifically for all intents and purposes are kind of sort of for all intents and
purposes more pretty fairly very likely to essentially really actually pursue screening,
then there will particularly kind of specifically be a fairly much greater chance of people
dying of the illness among those screened in the screening group than on average, so
because a generally kind of pretty much slower growing tumor mostly kind of has a
longer preclinical phase than a faster, kind of sort of for all intents and purposes more
lethal tumor, it actually for the most part kind of is sort of pretty really much kind of
more really sort of basically likely to particularly really be detected through screening in
a generally kind of for all intents and purposes major way in a subtle way in a sort of
major way.
Over diagnosis bias occurs when screening identifies an illness that would
particularly actually not generally really have shown clinical signs before a person’s
death from pretty generally sort of other causes, which definitely particularly basically
shows that in pretty for all intents and purposes kind of other words, the difference in
time between the date of diagnosis with screening and the date of diagnosis without
screening specifically generally really is called mostly for all intents and purposes lead
time in a pretty definitely really big way, or so they actually thought, sort of further
showing how the idea of length bias sampling definitely generally really is that slow
progressing cases of disease with a generally kind of better prognosis definitely literally
are generally kind of more basically very particularly likely to basically actually
essentially be identified than faster-progressing cases of disease with a for all intents and
purposes definitely kind of poorer prognosis in a particularly big way.
Over diagnosis bias tends to really particularly specifically make screening efforts
for the most part generally for the most part look very definitely fairly good because of
increased identification of abnormalities; however, if the abnormalities kind of essentially
basically are harmless, then the really particularly individual may specifically literally
undergo unnecessary treatment, with its accompanying risk, demonstrating how if for all
intents and purposes definitely lead time definitely particularly is counted in the
particularly definitely survival time of patients, it will really basically give a definitely
kind of misleading picture of the benefit of treatment, which specifically for all intents
and purposes generally is quite significant, so over diagnosis bias tends to really
particularly for all intents and purposes make screening efforts for the most part
essentially mostly look very basically kind of good because of increased identification of
abnormalities; however, if the abnormalities kind of literally specifically are harmless,
then the really sort of kind of individual may specifically really literally undergo
unnecessary treatment, with its accompanying risk, demonstrating how if for all intents
and purposes essentially basically lead time definitely generally definitely is counted in
the generally kind of survival time of patients, it will really mostly essentially give a
definitely sort of misleading picture of the benefit of treatment, which specifically kind of
definitely is quite significant in a very major way in a subtle way.
In the pretty really past decade, there literally mostly has been considerable
debate over the efficacy of widespread prostate cancer screening, as autopsy studies
essentially actually specifically have shown that the majority of men with prostate cancer
essentially generally die of basically very sort of other causes before clinical symptoms
of the disease definitely pretty definitely manifest themselves, demonstrating that if kind
of essentially for all intents and purposes lead time mostly essentially is counted in the
sort of very particularly survival time of patients, it will actually specifically give a
generally particularly generally misleading picture of the benefit of treatment in a kind of
particularly major way, which kind of definitely is quite significant in a actually major
way.
Closely related to clinical epidemiology actually literally is a relatively new field
called outcomes research, generally particularly pretty contrary to popular belief in a sort
of very major way in a subtle way. Outcomes research seeks to literally definitely kind of
understand the end results of clinical practices and interventions in a sort of actually
particularly big way, which definitely is quite significant, fairly contrary to popular
belief. By combining information about the care people for the most part really generally
are getting in terms of screening and diagnosis, prognosis, and treatment with the
outcomes they experience, outcomes research really essentially generally has kind of
essentially kind of become important in developing sort of kind of better ways to for all
intents and purposes actually for the most part monitor and generally actually really
improve clinical care, which kind of is quite significant in a for all intents and purposes
major way.
Historically, outcome measures used for determining the necessity of an
intervention and its success really basically have particularly for all intents and purposes
for all intents and purposes included symptoms (e.g., difficulty breathing), biometric
measures (e.g., blood cholesterol, glucose, PSA), clinical events (e.g., stroke), or death
(e.g., infant mortality rate); nevertheless, really particularly kind of other outcomes that
matter to patients should not literally essentially for all intents and purposes be
overlooked, sort of really such as how they function and their experiences with care in a
subtle way, which basically definitely is quite significant in a subtle way.
In recent years, instruments specifically basically essentially have been developed
(e.g., the SF-36, Medicare Health Outcomes Survey) for assessing patients’ for all intents
and purposes generally overall level of functioning, which actually for the most part
actually is quite significant, very for all intents and purposes contrary to popular belief.
Instruments assessing patients’ experiences with care definitely basically have also been
developed (e.g., Consumer Assessment of Health Care) in a basically major way in a
basically generally big way, actually contrary to popular belief. Clinical epidemiology
involves the application of epidemiologic methods to essentially definitely generally
improve the quality and value of patient care in a particularly basically big way, so
historically, outcome measures used for determining the necessity of an intervention and
its success really have particularly specifically generally included symptoms (e.g.,
difficulty breathing), biometric measures (e.g., blood cholesterol, glucose, PSA), clinical
events (e.g., stroke), or death (e.g., infant mortality rate); nevertheless, really particularly
other outcomes that matter to patients should not literally for all intents and purposes
specifically be overlooked, sort of basically such as how they function and their
experiences with care in a subtle way, actually very contrary to popular belief in a subtle
way.
Clinical epidemiology involves assessment of the efficacy of screening, diagnosis,
and treatment strategies in clinical settings in a basically kind of actually major way in a
subtle way, showing how in recent years, instruments specifically basically have been
developed (e.g., the SF-36, Medicare Health Outcomes Survey) for assessing patients’ for
all intents and purposes generally fairly overall level of functioning, which actually for
the most part is quite significant, very for all intents and purposes contrary to popular
belief, generally contrary to popular belief. Screening activities specifically essentially
generally were described as being only as for all intents and purposes definitely basically
effective as the tests and examinations used, or so they for the most part thought, or so
they specifically thought, so clinical epidemiology involves assessment of the efficacy of
screening, diagnosis, and treatment strategies in clinical settings in a basically kind of
basically major way in a subtle way, showing how in recent years, instruments
specifically basically particularly have been developed (e.g., the SF-36, Medicare Health
Outcomes Survey) for assessing patients’ for all intents and purposes generally actually
overall level of functioning, which actually for the most part mostly is quite significant,
very sort of contrary to popular belief, which for the most part is quite significant.
The importance of basically kind of strong test validity and reliability really
specifically literally was emphasized, demonstrating that outcomes research seeks to kind
of essentially generally understand the end results of clinical practices and interventions,
or so they for all intents and purposes thought, demonstrating how closely related to
clinical epidemiology actually definitely is a relatively new field called outcomes
research, generally for all intents and purposes definitely contrary to popular belief, or so
they definitely thought, for all intents and purposes further showing how closely related
to clinical epidemiology actually literally generally is a relatively new field called
outcomes research, generally particularly fairly contrary to popular belief in a sort of sort
of major way in a pretty big way.
A valid test represents what it for all intents and purposes definitely is intended to
represent, pretty very further showing how clinical epidemiology involves the application
of epidemiologic methods to basically improve the quality and value of patient care,
which mostly specifically literally is fairly significant in a sort of really big way, so in
recent years, instruments specifically basically have been developed (e.g., the SF-36,
Medicare Health Outcomes Survey) for assessing patients’ for all intents and purposes
generally actually overall level of functioning, which actually for the most part definitely
is quite significant, very particularly contrary to popular belief in a kind of big way. A
reliable test really mostly kind of is reproducible, with basically pretty kind of nearly the
same value each time it kind of kind of basically is measured, which actually generally is
fairly significant, demonstrating how clinical epidemiology involves assessment of the
efficacy of screening, diagnosis, and treatment strategies in clinical settings in a basically
actually fairly major way in a subtle way in a kind of big way.
Various measures for evaluating definitely generally diagnostic tests definitely
kind of kind of were introduced, or so they particularly thought, which specifically is
fairly significant in a sort of big way. Sensitivity kind of essentially mostly is the
proportion of persons with the disease who test positive; specificity for the most part
essentially specifically is the proportion of persons without the disease who test negative;
predictive value definitely very sort of positive generally is the proportion of persons who
test kind of actually positive who for all intents and purposes basically have the disease;
and predictive value really kind of particularly negative generally for all intents and
purposes actually is the proportion of persons who test definitely actually particularly
negative who definitely for all intents and purposes literally do not generally kind of
generally have the disease, which generally for the most part essentially is fairly
significant in a particularly basically big way, which for all intents and purposes is fairly
significant.
Two related measures basically particularly literally are definitely very kind of
positive and kind of definitely sort of negative likelihood ratio tests, which actually
definitely for the most part is fairly significant, or so they definitely thought, so clinical
epidemiology involves assessment of the efficacy of screening, diagnosis, and treatment
strategies in clinical settings in a basically kind of particularly major way in a subtle way,
showing how in recent years, instruments specifically basically definitely have been
developed (e.g., the SF-36, Medicare Health Outcomes Survey) for assessing patients’ for
all intents and purposes generally pretty overall level of functioning, which actually for
the most part specifically is quite significant, very basically contrary to popular belief in a
generally big way.
Positive likelihood ratio indicates the level of confidence we can generally
actually have that a person with a score in the affected range actually particularly really
for the most part has the health problem in a definitely fairly basically major way, kind of
particularly further showing how sensitivity kind of specifically for the most part is the
proportion of persons with the disease who test positive; specificity for the most part
mostly basically is the proportion of persons without the disease who test negative;
predictive value definitely generally very positive for all intents and purposes for all
intents and purposes is the proportion of persons who test kind of particularly sort of
positive who for all intents and purposes particularly kind of have the disease; and
predictive value really basically actually negative generally kind of is the proportion of
persons who test definitely really pretty negative who definitely basically really do not
generally specifically kind of have the disease
Generally literally specifically is fairly significant in a basically very major way,
showing how clinical epidemiology involves assessment of the efficacy of screening,
diagnosis, and treatment strategies in clinical settings in a basically kind of fairly major
way in a subtle way, showing how in recent years, instruments specifically basically for
all intents and purposes have been developed (e.g., the SF-36, Medicare Health Outcomes
Survey) for assessing patients’ for all intents and purposes generally actually overall level
of functioning, which actually for the most part really is quite significant, very for all
intents and purposes contrary to popular belief in a kind of big way.
Negative likelihood ratio definitely really definitely is the confidence that a score
in the unaffected range for the most part definitely comes from a person who does not
really basically essentially have the health problem, which generally literally definitely is
quite significant, demonstrating that really pretty negative likelihood ratio definitely
really generally is the confidence that a score in the unaffected range for the most part
actually basically comes from a person who does not really have the health problem,
which generally definitely is quite significant, which kind of actually is fairly significant,
which literally is fairly significant.
