Lecture 18 - Measure of association Flashcards
Measure of Association
Measure of association quantify the relation between exposure and outcome among the two groups
- For analytic study
Three MOA
- Relative Risk (Relative)
- Relative difference (Absolute)
- Odds ratio
Relative risk:
Calculation: Incidence in exposed / Incidence in unexposed
- Can use both IR and IP
- RR tells us the strength of the association (linkage or outcome and exposure)
The interpretation of RR
The exposed group were xx.xx times as likely to develop the outcome compared to comparison group
EVOC
Rules of RR
- RR>1
- RR=1
-RR<1
R>1
Meaning there is greater likelihood of the outcome in the exposed group
- Risk factor if the outcome is bad
R=1
No association
R<1
Greater likelihood of the outcome in the comparison group.
- Protective factor is the outcome is bad
Risk difference
Calculation: Incidence Exposed - Incidence unexposed
- can use both IR and IP
- Risk difference tells us the IMPACT of exposure - how much of the outcome is due to the exposure, and how much disease we would prevent by removing the exposure
Interpretation of Risk difference
There were an X cases per 100 people / per 100 person years of outcome in exposed group compared to unexposed group
VOEC
- There were x extra/fewer cases of outcome in exposed group compared to comparison group
3 Rules of RD
- RD>0
- RD=0
- RD<0
RD > 0
Same as RR but greater than 0.
- Meaning there is greater likelihood of the outcome in the exposed group
- Risk factor if the outcome is bad
RD=0
No association
RD<0
Same as RR but less than 0
- Greater likelihood of the outcome in the comparison group.
- Protective factor is the outcome is bad
Relative risk vs Relative difference
RR:
- Clues to causes
- Strength of association
RD:
- Impact of exposure
- Impact of removing exposure
