Chapter 4: Ecological Studies And Cross Sectional Studies

Question 1

What is an ecological study?

Answer 1

An ecological study is an observational study analysing at the population or group level, rather than an individual level. Used to measure prevalence and incidence of disease, particularly when the disease is rare.

Question 2

What does an ecological study indicate?

Answer 2

Maybe give potential clue regarding aetiology of diseases, in individuals.

Question 3

Advantages of an ecological study

Answer 3

• Often rely on secondary data (i.e. already exists)
• Relatively simple and inexpensive
• Analysis are generally simple to present and understand
• Good for hypothesis generation

Question 4

Disadvantages of an ecological study

Answer 4

• Alternative explanations fore results cannot be tested
• No individual-level data (i.e. cannot adjust for other factors)
• Ecological fallacy
• Cannot examine causality – a common limitation!

Question 5

Reasons to carry out an ecological study

Answer 5

• monitor population health strategies - may be developed and directed
• The purpose of the study is to make large scale comparison e.g comparison between countries
• The purpose of the study is to study the relationship between population-level exposure to risk factors and disease, or in order to look at the contextual effect of risk factors on the population
• Measurements at individual level are not available e.g. confidentiality might require that individuals are anonymised by aggregation of data to small area level; or
• The disease under investigation is rare, requiring aggregation of data for any analysis to be carried out

Question 6

Define ecological fallacy

Answer 6

the incorrect assumption that inferences can be made about an individual based on aggregate data for a group. It is a type of confounding specific to ecological studies.

Question 7

Types of ecological studies

Answer 7

• geographical
• longitudinal
• migration

Question 8

Define geographical ecological study

Answer 8

this type of study compares one geography with another by assessing the health of the population of each. Exposures for geographies may also be measures and included in analysis as well as other potential confounding variables such as demographic and socioeconomic informations.

Question 9

Define longitudinal study

Answer 9

a population is monitored to assess changed in disease over time. Again, confounding factors are often included in analysis

Question 10

Define migration ecological study

Answer 10

Data of migrant populations are collected and analysed. The unit of interest is neither time nor place but population type

Question 11

Analysis of ecological studies

Answer 11

• regression analysis is advisable to overcome confounding as with all observational studies
• multilevel modelling

Question 12

What are multilevel modelling

Answer 12

Multilevel modelling techniques have been developed, where analysis includes both individual and population level data, thus overcoming the ecological fallacy and enabling examination of contextual effects.

Question 13

Define migrant studies