POPH192 Lecture 20 - Case Control Studies Flashcards
are case-control studies an observational or an intervention study?
observational study
what are case-control studies designed for?
designed for rare/slow to develop outcomes
what do case-control studies examine?
can efficiently examine acute or transient exposures
what do case-control studies ascertain?
ascertain outcome status, then find out exposure(s)
- outcome to exposed?
- no outcome to exposed?
what are the 5 steps of creating a case-control study?
1) identify source population
2) identify people with the outcome (cases)
3) sample people without outcome from same population (controls)
4) measure exposure prior to outcome in cases and controls
5) compare odds of exposure to calculate measure of association: odds ratio (odds of exposure (cases)/ odds of exposure (controls)
what does it mean if the cases and controls are a good representation of the source population?
ratio of odds of exposure quantifies association between exposure and outcome
what does it mean if exposure is more likely in cases?
exposure is a potential risk factor
what does it mean if exposure is more likely in controls?
exposure is a potential protective factor
-exposure is not always bad
what does transient exposure measure?
only measures the relevant exposure period
what is the null value for the odds ratio?
1
when does the odds ratio (OR) approximately equal the relative risk (RR)?
when disease is rare, OR approximates the relative risk (rare disease assumption)v
-can interpret just like RR
what is the statement used for interpreting the odds ratio?
the EXPOSED GROUP were VALUE as likely to develop OUTCOME compared to COMPARISON GROUP
can controls measure the outcome?
controls don’t have outcome therefore they can not measure exposure
how case-control studies measure exposure?
index dates
what are index dates?
pretend control had event on the same date as the case (or at least close to it)
what are the 3 important points of case-control studies?
1) defined by outcome, so only one outcome
2) clear outcome defintion and identification
3) comprehensive case finding
do case-control studies use incidence or prevalent cases?
usually try to identify with incident cases
what are the 2 most important things for
control selection to be valid?
- need to represent the exposure distribution in source population
- must be capable of becoming a case (important for a control)
what are the limitations of a case-control study?
- usually can only study one outcome
- difficult to select appropriate control group
- can be susceptible to selection and recall bias
what are the strengths of a case-control study?
- rare outcomes, transient exposures
- multiple exposures
- temporal sequencing
- often comparatively quick and inexpensive
