Epidemiology (VI) Observational Studies

Question 1

What are the three main observational study types (3 C’s)?

Answer 1

Cohort, case-control, and cross-sectional

Question 2

How do cohort studies work?

Answer 2

A group (cohort) is followed over time and the incidence of a disease is compared with the risk factors in exposed and unexposed members.

Question 3

How do observational studies differ from experimental studies?

Answer 3

Observational studies are non-randomized

Question 4

What does it mean if the group in a cohort study that is not exposed to a risk factor has a higher incidence (incidence rate or cumulative incidence) of disease?

Answer 4

The exposure is protective.

Question 5

Should a cohort study’s study population be representative of the general population?

Answer 5

Yes, but those not at-risk should be excluded from the study; sometimes a group may be selected specifically for their exposure to some risk factor

Question 6

Must the exposure variable in a cohort study be dichotomous, categorical, or continuous?

Answer 6

It can be any of these

Question 7

What is an internal comparison group (cohort study)?

Answer 7

Nonexposed subjects within the cohort

– Preferable because the subjects were enrolled the same way as the exposed subjects, and the exposures and outcomes were measured via the same method for both groups

Question 8

What is an external comparison group (cohort study)?

Answer 8

A reference population or second cohort

(Necessary when all members of the cohort were exposed (e.g. all workers at a factory))

Question 9

Why are cohort studies useful?

Answer 9

An exposure (or multiple) can be associated with an outcome (or multiple)

Question 10

Which is generally preferable in a cohort study, internal or external comparison groups?

Answer 10

Internal (greater external validity)

Question 11

When are internal comparison groups necessary in cohort studies?

Answer 11

For rare exposures that would not be seen often in the general population

Question 12

What do cohort studies compare between groups?

Answer 12

Incidence levels

Question 13

Are individuals with the outcome being studied included at the start of a cohort study?

Answer 13

No, prevalent individuals are excluded

Question 14

What are three timing classifications of cohort studies (p, h, & a)?

Answer 14

Prospective, retrospective, ambidirectional

Question 15

What is the main rate used to assess risk in a cohort study?

Answer 15

Relative risk

Question 16

How is relative risk measured?

Answer 16

(Incidence_ExposedGroup)

/

(Incidence_{UnexposedGroup})