Cross-sectional and ecological

Question 1

What are two functions of experimental studies

Answer 1

• Study preventions and treatments for diseases

- Investigator actively assigns intervention (exposure)

Question 2

What are the two types of descriptive observational studies

Answer 2

Ecological: describe global rather than individual factors affecting outcome and/or exposure
Cross-sectional: determine outcome and exposure simultaneously

Question 3

What are the two types of analytical observational studies

Answer 3

• Cohort: follow people who have not had outcome yet over time to determine who has outcome
• Case-control: select a group of ill and a group of well people, determine whether they had exposure

Question 4

Most cross-sectional studies are

Answer 4

surveys

Question 5

Many observational studies are…

Answer 5

cross-sectional

Question 6

What are cross-sectional studies

Answer 6

• Exposure and disease measures can be obtained at the individual or group level
• Snapshot of the population at a certain point in time
• Exposure and disease information collected simultaneously

Question 7

What are some uses of cross-sectional studies?

Answer 7

• -Estimation of the magnitude and distribution of a health problem
• -Planning health services and administering medical care facilities, and other intervention planning
• -Examine trends in disease or risk factors that can vary over time
• -Report associations and generate hypotheses

Question 8

draw the 2x2 table, what studies is it used with?

Answer 8

cross-sectional studies

Question 9

What are some advantages of cross-sectional studies?

Answer 9

Advantages (uses)
Inexpensive
Easy to conduct
Magnitude and distribution of health problems
Trends of disease or risk factor
Obtain many associations at once
Hypothesis generating

Question 10

What are some disadvantages of the cross-sectional studies?

Answer 10

Disadvantages
Identifying prevalent cases, not incident cases
Hard to study low prevalence diseases
Non-response bias – people who respond to questionnaire are systematically different than those who do not
Not possible to establish temporality
In isolation, difficult to establish causality

Question 11

What are two types of analytical observation studies?

Answer 11

Observational Studies – Analytical:
Cohort: follow people who have not had outcome yet over time to determine who has outcome
Case-control: select a group of ill and a group of well people, determine whether they had exposure

Question 12

What are the six elements of ecologic studies?

Answer 12

-Completely ecologic study: both exposure and outcome analyzed at group level
-Partially ecologic study: either exposure or outcome analyzed at group level
-Can be used for generating hypotheses and for causal inference depending on the research question
-Did the Australia firearm buyback cause a decrease in firearm homicide?
-Most are cross-sectional
-Generally makes use of secondary data
Compare between groups and/or over time

Question 13

Reasons for conducting an ecologic study

Answer 13

Quick, simple, inexpensive
Good for generating hypotheses and sometimes causal inference
Some variables are only defined/measured for groups
Sometimes question is about group differences, not individual differences, which require group-level data
Sometimes ignoring group-level factors may lead us to incorrect inferences (e.g., important impact of “context”)

Question 14

Two functions of ecologic study

Answer 14

By comparing groups (e.g. countries) ecologic studies allow us to study a greater range of exposures
If diet varies very little within countries, it may not appear to be an important risk factor for CHD The true effect of CHD can only be seen by comparing countries with very different diets

Question 15

What is the ecological fallacy?

Answer 15

• Observations made at group level may not represent exposure-disease relationship at individual level
• Ecologic fallacy occurs when incorrect inferences about individuals are made from group level data
• Implication: Conclusions obtained from ecologic study may be weaker or even the reverse of those from a study that collects data on individual subjects

Question 16

Limitations of ecologic study

Answer 16

• May not be a lot of heterogeneity between groups
• Possible imprecise measurement of individuals’ exposure and disease
• Smaller sample sizes
• Atomistic fallacy is making group-level inference from individual-level observations
• High-income individuals are less likely to have heart disease; therefore, high-income countries are less likely to have high rates of heart disease.