lecture 20 Flashcards
what are case control studies
- identify people with outcome
- find people without outcome
- compare exposure likelihood beforehand
what are the steps of case control studies
- identify a source population
- identify people with the outcome (cases)
- sample people without the outcome (controls)
- measure exposure prior to outcome
- compare odds of exposure
what do case control studies measure
is the exposure more or less likely in people with the outcome (case) than without (controls)
what is the odds ratio
how many times as likely cases are to have the exposure compared to controls
what is the null value of odds ratio
1
- where the odds of the exposure will be the same in the cases and in the controls
how to calculate the odds ratio
odds of exposure in cases / odds of exposure in controls
how to interpret the odds ratio
the EXPOSED GROUP were VALUE as likely to develop OUTCOME compared to COMPARISON GROUP
what is important about case selection in case control studies
- usually try to identify incident cases (new cases of the disease
- can not always do that, sometimes you just recruit people with the outcome (cases that exist)
- only one outcome per study = really clearly defined
what is important about the control selection of a case control study
- need to represent the exposure distribution of people with the outcome in the source population = for the comparison to be valid
- controls must be capable of being a case
whats important about exposure measurements in case control studies
they must be comparable
what are the strengths to case control studies
- rare outcomes, transient exposures
- multiple exposures
- temporal sequencing
- often comparatively quick and inexpensive
what are the limitations of case control studies
- usually can only study one outcome
- difficult to select appropriate control group
- can be susceptible to recall bias
