Cohort Study Design

What is a cohort study design?

an observational research method that follows a group of people overtime

What are the strengths of a cohort study design?

1. Proves temporality

2. Good for rare exposures

3. Tracks many things at once: can look at multiple health outcomes simultaneously

4. Prospective study: can look forward in time, and get “real-time” data, rather than relying on memory

What are the challenges of a cohort study design?

1. High cost and takes a long time

2. Lost to follow-up; people move, change phone numbers; this can bias results, undermine validity

3. Changing behaviors/environment: participant might change health behavior, which can be hard to measure the initial exposure

4. Confounding issues

5. Not ideal for studying rare diseases

Since individuals are followed over time, what measure of disease can we calculate?

Incidence

What are the 2 types of cohorts?

1. General Cohorts

2. Special Cohorts

What is a general cohort?

They investigate exposures that are common in the general population (smoking, high blood pressure)

What is a special cohort?

Investigate unusual or rare exposures

What are sources of exposure information that can be used for cohort studies?

Pre-existing records, questionnaires + interviews, and direct testing

What are the different types of cohort studies?

1. Concurrent

2. Retrospective

What is a concurrent cohort study?

• prospective, longitudinal

• Investigator follows subjects concurrently (currently) through calendar time

What is a retrospective cohort study?

• historical, nonconcurrent prospective

• Exposure is obtained from records, the outcome has already occurred, but you must determine that the exposure occurred prior to disease development

What are the characteristics of a prospective cohort study?

1. more expensive, time-consuming

2. used for rare exposures

3. not used for diseases with long latent periods (takes a long time for the disease to develop)

4. Less vulnerable to bias

What are the characteristics of a retrospective cohort study?

1. cheaper, faster

2. used for diseases with a long latent period (disease has already occured; not waiting for it to develop

3. More vulnerable to bias

What is the only valid way to be “out” of a cohort study?

if a participant develops the disease while the study is happening, if they die, or if the study ends.

Attrition or loss to follow up raises doubts about the _____ of a study.

Validity