Ecological Studies Studies of group not individual characteristics Data from

Ecological studies studies of group not individual

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Ecological Studies Studies of group (not individual) characteristics Data from cities, countries Each point uses the mean (average) values for a population Low cost, simple and convenient Creates a scatter plot Measure of association is a correlation Ecological fallacy – assuming an exposure is causal because it is prevalent in the same population that has a high prevalence of a certain outcome
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Copyright © 2018 Cognella, Inc. Each data point represents a country Ecological Study
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Copyright © 2018 Cognella, Inc. Ecological Studies Trend suggests that poor air quality is associated with an increased rate at COPD at the population level This evidence does not prove poor air quality causes COPD at the individual level If we did conclude this, it would be an ecological fallacy Group associations do not necessarily hold at the individual level
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Copyright © 2018 Cognella, Inc. Cross-sectional/Prevalence Studies Conducted over a short period of time (usually a few days or weeks) Unit of analysis is the individual There is no follow-up period Measures outcome and exposure at the same time Can be conducted at the start of a cohort study to gather baseline data A “snapshot” of the health status of a population in a particular point in time
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Copyright © 2018 Cognella, Inc. Cross-sectional/Prevalence Studies Can provide evidence of the need for analytic epidemiologic study Can be used to study several associations at once Can be conducted over a short period of time Produces prevalence data
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Copyright © 2018 Cognella, Inc. Disease No Disease Total Exposed a b a+b Not exposed c d c+d Total a+c b+d a+b+c+d 2x2 Table
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Copyright © 2018 Cognella, Inc. Cross-sectional/Prevalence Studies a = the number of individuals who have the disease and are exposed b = the number of individuals who do not have the disease but have been exposed c = the number of individuals who have the disease but who have not been exposed d = the number of individuals who do not have the disease and have not been exposed
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Copyright © 2018 Cognella, Inc.
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