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CHAPTER 6

Problems and Limits of Epidemiology

Problems with Studying Humans

Intervention study problem:

Subjects may not follow prescribed behavior throughout study period.

Cohort study problem:

Sometimes it is hard to isolate which of many factors are responsible for health differences.

Case-control study problems:

Control group may not be truly comparable.

Errors may exist in reporting or recalls.

For all studies, differential drop-outs are worrisome.

Sources of Error

Random variation

Confounding variables

Bias

Selection bias

Reporting bias or recall bias

Factors That Lend Validity to Results

Strong association

Dose–response relationship

Known biological explanation

Large study population

Consistent results from several studies

High relative risk or odds ratio

Hormone Replacement Therapy

Conflicting results exist between two major studies.

Previous positive evidence has all come from observational studies.

Clinical trial is the gold standard.

Results of cohort study were confounded by associated factors that made women taking HRT healthier, even without the therapy.

Ethical Issues

Nazi experiments on humans

Tuskegee syphilis study

AIDS epidemic

Bone marrow treatment for advanced breast cancer

New rules

Informed consent

Institutional review boards

Importance of clinical trials

Possibility of conflict of interest with medical providers who stand to profit

Conflicts of Interest in Drug Trials

Drug companies are required to conduct randomized controlled trials on a new drug before it can be approved.

Harmful side effects have frequently become obvious after drugs were approved.

There is evidence that drug companies sometimes suppress negative findings.

All clinical trials must now be registered in advance with a public database.

Discussion Question 1

What are strengths and weaknesses of each of the major types of epidemiologic study?

Randomized controlled trial

Cohort

Case-control

Discussion Question 2

Have you heard of the Tuskegee syphilis study?

Why was it unethical?

What influence has it had on the conduct of clinical trials?

Discussion Question 3

Visit the website of the Hastings Center, www.thehastingscenter.org.

What issues is the Hastings Center concerned with this month?