Study Designs: Observational Studies

Question 1

Starting from the best, describe the pyramid of 3 observational study designs.

Answer 1

Cohort studies

Case-control studies

Cross-sectional studies

Question 2

Describe the structure of a cohort study.

Answer 2

Participants are grouped based on exposure (e.g. smoking vs non-smoking) and followed over time to observe outcomes (e.g. lung cancer incidence)

Question 3

List 2 strengths of cohort studies.

Answer 3

Good for rare exposures

Can measure multiple outcomes simultaneously

Question 4

List 2 limitations of cohort studies.

Answer 4

Time-consuming and costly

Risk of loss to follow-up

Question 5

What are the 2 types of cohort studies?

Answer 5

Retrospective and prospective

Question 6

What is the interpretation of cohort studies?

Answer 6

Risk of (outcome) in (exposure group) is (RR) times that of (non-exposure group)

Question 7

In cohort studies, when is the CI statistically significant?

Answer 7

When it excludes 1

Question 8

In cohort studies, when is the p value statistically significant?

Answer 8

When it is <0.05

Question 9

Describe the structure of case-control studies.

Answer 9

Participants are selected based on the presence (cases) or absence (control) of a specific outcome, and past exposures are compared

Question 10

List 2 strengths of case-control studies.

Answer 10

Good for rare outcomes

Good for diseases with long latent periods

Question 11

List 2 limitations of case-control studies.

Answer 11

Cannot establish incidence or prevalence

Potential recall bias

Question 12

What is the interpretation of case-control studies?

Answer 12

Odds of (exposure) in (cases) is (OR) times that of (controls)

Question 13

Describe the structure of cross-sectional studies.

Answer 13

Data is collected at a single point in time to assess exposure and outcome prevalence simultaneously

Question 14

List 2 strengths of cross-sectional studies.

Answer 14

No follow up needed

Quicker and cheaper than cohorts and case-control

Question 15

List 2 limitations of cross-sectional studies.

Answer 15

Cannot establish causation

Potential reverse causality

Question 16

Describe the structure of ecological studies.

Answer 16

Examines relationship between exposure and outcomes at the group or population level rather than the individual level

Question 17

Name a strength of ecological studies.

Answer 17

Good for hypothesis generation

Question 18

List 2 limitations of ecological studies.

Answer 18

Hard to control for confounders

Ecological fallacy – concluding that associations at group level mean they also exist at individual level