Lecture 17: Cross-Sectional and Ecological Studies Flashcards
What are the two study designs in epidemiology?
Descriptive and analytic
What is descriptive epidemiology?
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
What four core questions are asked in descriptive epidemiology?
- What (diseases are occurring)?
- Who (is getting them)?
- Where?
- When?
What is analytic epidemiology?
It looks at associations between exposures and outcomes and allows us to look at potential causal agents
Are cross sectional studies an example of descriptive or analytic epidemiology?
descriptive
What is a cross sectional study?
A study that measures the exposures and/or outcomes at one point in time
What is the purpose of a cross-sectional study?
To look at the relationship between an exposure and a health outcome
What measure of association do cross-sectional studies measure?
prevalence
What four things can cross sectional studies be used for?
- describing prevalence
- compare prevalence
- generate a hypothesis
- plan
Describe the composition of the GATE frame
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.
What are some limitations of cross sectional studies?
- 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)
What are some strengths of the cross sectional studies?
- addresses multiple outcomes at once
- can calculate prevalence and distribution of prevalence
- cheap and quick
- good for hypothesis generation
Cross sectional studies measure both _________ and __________ at the same time
outcomes
exposures
How is a cross sectional study normally conducted?
As a survey
What does an ecological study do?
compares exposures and outcomes across groups not individuals
What three things can ecological studies be used for?
- to compare between populations
- to assess population level factors
- to consider hypothesis
What are the strengths of ecological studies?
- it works at the population level
- good for hypothesis generation
- cheap
- quick
What are some weaknesses of ecological studies?
- ecological fallacy
- can’t control for confounding
- can’t claim causation
- not able to calculate measures of association
What is ecological fallacy? Give an example
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
Cross sectional studies and ecological studies are what types of studies?
descriptive and observational
