cross-sectional + ecological studies

Question 1

what is the purpose of a cross-sectional study?

Answer 1

to estimate the frequency or outcome at a particular point in time.

Question 2

what is a descriptive cross-sectional study?

Answer 2

describes frequency of exposure or outcome in a defined population.

Question 3

what is an analytical cross-sectional study?

Answer 3

simultaneously collects information on both the outcome of interest and potential risk factors in a defined population.

then compare the prevalence of the outcome in the people exposed to each risk factor with the prevalence in those not exposed.

Question 4

when would you use a cross-sectional study?

Answer 4

• Health service planning - prevalence of specific outcome in a defined population in time.
• useful for assessing burden of disease and planning preventative and curative services.
• generate hypotheses about causes
  (association with current risk factors)
  (association with past exposure of early clinical signs)

Question 5

what are the methods used to collect data in cross-sectional studies?

Answer 5

• survey sampling

Question 6

what are the 2 main sources of bias in cross-sectional studies?

Answer 6

• selection bias
• recall bias

Question 7

how can bias be minimised in cross-sectional studies?

Answer 7

• can minimise by having strict case definition for the outcome of interest
• by using standardised methods of data collection
• by ensuring that the researcher who assigns the diagnosis is not aware of exposure status.

Question 8

what are the advantages of x-sectional studies?

Answer 8

• easy and economical
• provides important info on the distribution and burden of exposures and outcomes - valuable for health-service planning
• can be used as the first step in the study of possible exposure-outcome relationship.

Question 9

what are the disadvantages of cross-sectional studies?

Answer 9

• measures prevalence rather than incident cases - limited value for investigating etiological relationships
• can be difficult to establish the time-sequence of events in a x-sectional study.
• reverse causality

Question 10

what is an ecological study?

Answer 10

an observational study with populations or groups (instead of individuals) being unit of observation.

compares group averages
- health
- risk factors

Question 11

what are ecological studies used for?

Answer 11

• describing associations at a group level
• quick and cheap routine data
• generates hypotheses - first step

Question 12

what is ecological fallacy?

Answer 12

an attempt to infer from the ecological level (group level) to individual level