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Observational Studies (Analytical) (Case-Control Studies (It often can NOT…
Observational Studies (Analytical)
Properties
• It
has
a comparison group
• Hypothesis-Testing
• It quantifies
associations between exposures and outcomes
by comparing
exposed/unexposed
or diseased/non-diseased
• It does
not
manipulate the exposure
Cohort Studies
It directly
measures
INCIDENCE
and
RISK
It
compares
Exposed
and
Unexposed
People are classified on the basis of the
presence or absence of exposure to a particular factor
then
followed for a specified time period to determine the development of disease
in each exposure group
’Start with
Exposed
and
Unexposed
’
Well-suited for rare exposures
Can examine multiple effects of a single exposure
Usually Prospective (
looking forward in time
)
Subjects must be
free of the health outcome at time their exposure status is determined
Able to demonstrate the temporal relationship between exposure and health outcome
Case-Control Studies
It often
can
NOT
directly
measure INCIDENCE
and
RISK**
It
compares
DISEASED
and
NON-DISEASED
It needs to use techniques to estimate these parameters
It looks for
past exposure factors
They (often) measure
PREVALENCE
and
ODDS
It starts with the
identification of individuals with the disease and a suitable control
‘Start with
Cases
and
Controls
’
They’re able to assess the relationship of a wide range of exposures with the disease
They are good for the study of diseases with long latent periods and/or rare diseases.
Vulnerable to Bias
It can be tricky to establish a temporal relationship between the exposure and outcome
Control selection can be very difficult and should be representative of the source population that gave rise to the cases