Lecture 17: Cross sectional and ecological studies

Question 1

What is a cross-sectional study and what do they measure and why are they used?

Answer 1

Measure exposures and/or outcomes at one point in time

Measure prevalence (affected by incidence and duration)

Can assess multiple exposures and outcomes

Used to:
- describe prevalence
- compare prevalence
- generate hypotheses
- plan (e.g. health service delivery)

Question 2

What are some limitations of cross sectional studies?

Answer 2

Hard to determine temporal sequencing of events (outcome or exposure first)

Measures prevalence not incidence

Not good for studying rare outcomes or exposures

Not good for assessing variable and transient exposures or outcomes

Question 3

What are ecological studies and what are they used for?

Answer 3

Compare exposures and outcomes across GROUPS not individuals

To compare between populations
To assess population level factors
To consider hypotheses

Question 4

What are some limitations of ecological studies?

Answer 4

Ecological fallacy - derives from ascribing to individuals the characteristics of the group.

Cannot control for confounding
Cannot show causation