7 - Ecological and cross-sectional studies

Question 1

Ecological study

Answer 1

Measures disease frequencies in relation to population exposures
Is an observational study

Question 2

Cross-sectional studies Advantages / Disadvantages

Answer 2

Cheap, simple, safe
Prevalence not incidence
Association not causality
Recall bias susceptibility
Confounders may be unequally distributed

Question 3

Repeated surveys

Answer 3

Can identify time trends
eg multiple rounds covid swabs
Annual Health Survey for England
Different individuals surveyed each time - hence not a cohort

Question 4

Ecological Studies Advantages / Limitations

Answer 4

Quick, cheap
Association not causation
Confounders
Ecological fallacy

Question 5

Ecological Fallacy

Answer 5

An association observed between variables on an aggregate level does not necessarily represent the association that exists at an individual level…..
Correlated pieces of information may not have been measured on the same people

Question 6

Cross-sectional studies commonly used to

Answer 6

Calculate Prevalence for health care planning
Determine the distribution of factors within the population eg demographics, drinking
Estimate levels of common conditions with longer duration
eg LTCs, serological status
Data collected from cross-sectional surveys are often used in ecological studies

Question 7

Ecological Studies

Answer 7

In ecological studies the unit of observation is the population or community. Disease rates and exposures are measured in each of a series of populations and their relation is examined.
Often the information about disease and exposure is abstracted from published statistics and therefore does not require expensive or time consuming data collection.

Question 8

Correlation Analyses for Ecological Survey

Answer 8

The Pearson correlation coefficient provides a measure of the strength of linear association between two variables
eg GDP per capita vs infant mortality by country