Lecture 8 - Measures of Association: How large is the effect? Flashcards
What does measuring incidence also measure?
Absolute Risk
What is required for measuring incidence?
To follow a group of people at risk for a period of time
What are the best study designs to measure incidence?
- RCT
- Cohort
What does a Relative Risk > 1 mean?
“exposure” increases the likelihood of the outcome
What does a Relative Risk < 1 mean?
“exposure” decreases the likelihood of the outcome
What does a Relative Risk = 1 mean?
“exposure” has NO effect on the outcome
Define Relative Risk Reduction (RRR)
RRR is the proportional reduction in the event rates between experimental and control patients
What are the two ways to calculate RRR?
RRR = 1 - RR
RRR = [Control Event Rate - Exp Event Rate]
What are problems with RRR?
- They make results sound more impressive than they are
- RRR cannot discriminate between very large and very small treatment effects
- They do not consider the baseline risk of patients in a trial having a particular outcome
What does Relative Risk (RR) tell us?
Measure of strength of association; often of interest to epidemiologist who do etiologic research
What does Absolute Risk (AR) tell us?
If casualty exists, then AR tells us the potential impact the results have on individuals or communities
What are Numbers Needed to Treat (NNT) relevant for?
Understanding clinical decisions
What is NNT?
The number of patients that need to be treated in order for 1 extra patient to benefit
What is the formula for NNT?
NNT = 1 / ARR
