SAC360

1. Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com.
CHAPTER 6
Problems and
Limits of
Epidemiology

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
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.

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
Sources of Error
 Random variation
 Confounding variables
 Bias
– Selection bias
– Reporting bias or recall bias

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
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

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
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.

6. Copyright
©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
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

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
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.

8. Copyright
©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
Discussion Question 1
 What are strengths and weaknesses of each of the major types of
epidemiologic study?
– Randomized controlled trial
– Cohort
– Case-control

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
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?

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©
2021
by
Jones
&
Bartlett
Learning,
LLC
an
Ascend
Learning
Company.
www.jblearning.com
Discussion Question 3
 Visit the website of the Hastings Center, www.thehastingscenter.org.
 What issues is the Hastings Center concerned with this month?