Inci_Pre 222

PUBH 380: Measures of Morbidity – Incidence and Prevalence

Homework 2 (30 points)

NAMES:___________________________________

1) A cohort of 10,000 subjects thought to be at increased risk for Breast Cancer (BC), were enrolled in a three-year study in January 1997. At the initial examination on January 1st, 1997, 32 subjects were found to have BC already, 12 of whom died by the end of the study.

· During 1997, 60 cases were subsequently diagnosed, 30 of whom died by the end of the study. Additionally, there were 45 other losses during 1997 for other reasons (deaths from other causes, withdrawal).

· 52 cases were diagnosed in 1998, 9 of whom died, and there were 7 other losses to follow-up during the year.

· 24 cases were diagnosed in 1999, all of whom were still alive at the end of the study. 30 individuals were lost to follow-up for other reasons during 1999.

· Other than the deaths and losses mentioned, the population remained stable during the period, i.e. those enumerated above were the only deaths, refusals or other losses to follow-up.

Use the table below to keep track of deaths and losses for calculations.

Time	initial number (at the beginning of that period)	# persons with BC	fatal cases	lost to follow-up
Start	10,000	32	12	0
1997	9,968
1998
1999
end

Calculate and provide an interpretation for each of the following. Each calculation will be scored as follows so be sure to show your work and provide an interpretation to your answers! 5 points (1 for formula, 1 for numerator, 1 for denominator, 1 for correct answer, and 1 for interpretation)

a) The baseline prevalence of Breast Cancer in this sample. (5 points)

b) The one-year cumulative incidence (incidence proportion) of Breast Cancer for each of the three years, taking into account losses in each year. (15 points)

c) The three-year cumulative incidence (incidence proportion) for Breast Cancer, (from Jan 1997, to Dec. 1999), taking into account losses over the three-year period. (5 points)

d) The incidence density for the three-year period and express it in terms of 1000 person-years of observation. Assume losses took place and cases were diagnosed at the midpoint of the period in which they occurred. (5 points)

2) Which measure was reported in each of the following examples? Your options include: prevalence, cumulative incidence, or incidence density. (5 points)

a. In 1994, 26% of Americans had high blood pressure (U.S. Department of Health and Human Services, 1994).

b. 17.9% of female survey respondents between the ages of 14 – 15 reported having had an eating disorder during some period in her life.

c. During an outbreak of cholera in Africa in 1985, the average risk of contracting this disease was 12.6%.

d. There were 2 deaths out of 16 breast cancer patients during a study period that resulted in 240 months of follow-up for all cases.

e. 0.58% of the elderly living in South Florida in 1999 caught influenza between the months of September through December.