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Cohort studies
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Case control studies
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Suited for rare diseases
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No
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Yes since starting with a set of cases
|
|
Suited for rare exposures
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Yes since starting with exposure status
|
No
|
|
Allows for studying several exposures
|
Difficult but examples exists
(Framingham study)
|
Yes
|
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Allows for studying several outcomes
|
Yes
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No
|
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Disease status easy to ascertain
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Sometimes difficult
|
Easier since starting point of the study
|
|
Exposure status easier to ascertain
|
Yes since starting point of the study.
Except for retrospective cohorts
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Sometimes difficult.
Information biases.
|
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Allows computation of risk and rates
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Yes
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No
|
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Allows computation of effect
|
Computation of risk ratio
and rate ratio
|
Estimation of risk ratio, rate ratio
from odds ratio
|
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Allows studying natural history of disease
|
Yes
Easier to show that cause precedes effect.
|
More difficult
Temporality between cause and effect difficult to establish
|
|
Based on existing data sources
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Difficult
|
Yes but access to information sometimes difficult
|
|
Easiness to find a reference group
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Usually not difficult to identify an unexposed population
|
No
Major potential biases when selecting a control group
|
|
Sample size
|
Large
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Small
|
|
Cost
|
Elevated
except if retrospective cohorts
|
Smaller
|
|
Time required
|
Long, sometimes very long except if retrospective cohorts
|
Shorter
|
|
Follow up
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Difficult, loss to follow up
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No follow up
|
|
Logistics
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Heavy
Many staff, large data sets
Long duration
|
Easier
|
|
Concept
|
Easy to understand
|
Difficult to understand particularly if case cohort or density case control study
|
|
Ethical issues
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Major if studying risk factors.
Interruption of study if exposure shown to be harmful.
Need for intermediate analysis.
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None since outcome already happened.
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