Lecture 20 - Case control studies Flashcards
Case control study is
Analytic, observational studies
work backwards - we start with participants with known outcome status
Case controls studies address some of the issues with doing a cohort study
- Designed for rare/slow outcomes
- Can efficiently examine acute or transient exposures
cases vs controls
cases - outcome
controls (without outcome)
case control works by
- identifying people with outcome
- Find people without outcome
- Compare exposure likelihood beforehand (odds)
Steps of case control study
- Identify source population
- Identify people with outcome (cases)
- Sample people without outcome from same population (controls)
- Measure exposure prior to outcome in cases and controls
- Compare odds of exposure to calculate measure of association (odds ratio)
MOA in case control
Odds ratio
- as cannot calculate incidence of outcome
- How many times as likely cases are to have the exposure compared to controls
Interpreting the OR
People with outcome are x times as likely too have had the exposure than people without the outcome
EVOC (RR)
Strengths of Case control
- Good for rare outcome and trasnient exposures
- Can assess multiple exposures
- Temporal sequencing
- Quick and inexpensive
Limitations
- Can only study one outcome
- Difficult to select an appropriate control group
- Prone to selection and recall bias
Index dates
can be used for transient exposure in controls who didn’t have an associated event - the exposure is measured on the same date as the case
Case selection
usually try to identify incident cases
Control Selection
- Often select multiple control per case for statistical power
- must also be capable of becoming a case
Exposure measurement
Exposure measurements must be comparable
- Dead cases vs alive controls
- Interviewers may act differently for cases and controls
- Cases trying to work out what made them sick
- Outcome may affect recall ability
Case control finds?
It finds outcome status then finds out exposures
