20 Flashcards
Types of analytic studies
Limitations of cohort studies
- Can be inefficient with rare/slow to develop outcomes
- Can be inefficient with transient/acute exposures
Alternatives to the limitations of cohort studies
Historical cohort studies
Case-control studies
What issues can case-control studies address that cohort studies can’t?
- Designed for rare/slow to develop outcomes
- Can efficiently examine acute or transient exposures
Cohort studies vs case-control studies
COHORT:
Measure exposure status
Follow over time
Compare development of outcome (incidence)
CASE-CONRTOL
Identify people with outcome
Find people without outcome
Compare exposure likelihood beforehand (odds)
Case-control studies diagram
Logic of case-control studies
Is the exposure more or less likely in people with the outcome (cases) than without (controls)?
Step by step of a CASE CONRTOL study
- Identifying source population
- Identify people with outcome (cases)
- Same people without outcome from the same population (controls)
- Measure exposure prior to outcome in cases and controls
- Compare odds of exposures to calculate measure of association (odds ratio)
In case-control studies what measure of association is used ?
Odds ratio
Why is the odds ratio used
Can’t calculate incidence of outcome
Have selected number of people in study with and without outcome
Odds are not a measure of ……
Occurrence
Odds ratio features
Measure of association
- Ratio of odds instead of incidences
- How many times as likely cases are to have the exposure
compared to controls
Interpretation of the odds ratio vs the relative risk
WHEN A DISEASE IS RARE…
Fortunately… OR ≅ RR
- When disease is rare, OR approximates the RR ( rare disease
assumption)
- Can interpret OR just like RR
Use RR interpretation in this course???? Wtf does that mean?!!!?
Interpreting the odds ratio - 4 key things
- exposed group
- value
- outcome
- comparison group
- use RR interpitation