Lecture 17: Cross-Sectional and Ecological Studies

Question 1

What are the two study designs in epidemiology?

Answer 1

Descriptive and analytic

Question 2

What is descriptive epidemiology?

Answer 2

It is observational and looks at the person, place and time. It allows you to describe what is happening in terms of a particular health outcome or exposure

Question 3

What four core questions are asked in descriptive epidemiology?

Answer 3

1. What (diseases are occurring)?
2. Who (is getting them)?
3. Where?
4. When?

Question 4

What is analytic epidemiology?

Answer 4

It looks at associations between exposures and outcomes and allows us to look at potential causal agents

Question 5

Are cross sectional studies an example of descriptive or analytic epidemiology?

Answer 5

descriptive

Question 6

What is a cross sectional study?

Answer 6

A study that measures the exposures and/or outcomes at one point in time

Question 7

What is the purpose of a cross-sectional study?

Answer 7

To look at the relationship between an exposure and a health outcome

Question 8

What measure of association do cross-sectional studies measure?

Answer 8

prevalence

Question 9

What four things can cross sectional studies be used for?

Answer 9

• describing prevalence
• compare prevalence
• generate a hypothesis
• plan

Question 10

Describe the composition of the GATE frame

Answer 10

From the population (source), we take a sample. Of the sample, there are people that are exposed (exposure group) and people that are not (comparison group). From each of those two groups, there are people who develop the outcome and those that do not.

Question 11

What are some limitations of cross sectional studies?

Answer 11

• there is no temporal sequence (ie. we don’t know whether the exposure or outcome came first) so we can no claim causation
• we can not measure incidence
• we can not use any measures of association
• not good for rare outcome or exposures
• not good for transient exposures (things that can come and go like colds)

Question 12

What are some strengths of the cross sectional studies?

Answer 12

• addresses multiple outcomes at once
• can calculate prevalence and distribution of prevalence
• cheap and quick
• good for hypothesis generation

Question 13

Cross sectional studies measure both _________ and __________ at the same time

Answer 13

outcomes

exposures

Question 14

How is a cross sectional study normally conducted?

Answer 14

As a survey

Question 15

What does an ecological study do?

Answer 15

compares exposures and outcomes across groups not individuals

Question 16

What three things can ecological studies be used for?

Answer 16

1. to compare between populations
2. to assess population level factors
3. to consider hypothesis

Question 17

What are the strengths of ecological studies?

Answer 17

• it works at the population level
• good for hypothesis generation
• cheap
• quick

Question 18

What are some weaknesses of ecological studies?

Answer 18

• ecological fallacy
• can’t control for confounding
• can’t claim causation
• not able to calculate measures of association

Question 19

What is ecological fallacy? Give an example

Answer 19

We are measuring prevalence at a population level and can’t make the assumption at an individual level. For example, if we find that wealthier countries have a higher alcohol consumption, it does not mean that wealthier people have a higher alcohol consumption

Question 20

Cross sectional studies and ecological studies are what types of studies?

Answer 20

descriptive and observational