Cohort Study

Objectives

• To discuss cohort study designs

• To discuss data from some cohort studies

Cohort Design

• Observational

• Classified by exposure and non-exposure

• Patients are followed to outcome

• Can get incidence rates of outcome

• Relative risk is the measure of association

Cohort Study Design

Critique of Studies

• Purpose of study and public health significance

• Study sampling• Study design• Threats to validity• Unit of analysis and type of analysis• Results (discuss tables)• Discussion and conclusion

Example 1 – Retrospective Cohort

Example 2 –Quasi-experimental design

Example 3 –prospective cohort• Scenario: Since prophylaxis against perinatal HIV

transmission was recommended by the Centers for Disease Control and Prevention in 1994, the perinatal transmission rate has declined substantially. There is now an initiative to eradicate perinatal transmission of HIV. The protocol calls for administration of zidovudine (ZDV) during the prenatal period, during the delivery period and then during the six weeks after delivery (i.e. the child receives ZDV drops 4 times a day for 6 weeks). Adherence to this protocol is essential for eradication to become a reality. The CDC wants to develop an intervention study to improve adherence to ZDV among exposed infants during the 6 weeks post delivery period. You are the epidemiologist and are on the committee to develop this study. Please address the following.

Exercise

1. Briefly discuss the public health importance of this study.

2. What intervention will you choose and what study design will you perform to test the efficacy of this intervention?

3. What type of sample size will the study require and will you have any selection criteria for enrollment into the study?

4. Discuss any ethical considerations that may arise as a result of this study.

• Discuss any potential threats to the validity of this study