Lecture 3: Measures of Association Flashcards
2 types of measures of association
Exposure and outcome
Be able to draw exposure/outcome table!
(see powerpoint)
Outcome predicted if SAME group of exposure did not have exposure in the first place. Assumes non-exposed group is EQUAL and EXCHANGEABLE/COMPARABLE to exposed group.
Counterfactual theory
What measure will always be in the columns in the measure table?
Outcomes/disease!
Difference in frequencies/counts (simple subtraction)
Absolute difference
Ratio of frequencies/counts or proportions (simple division)
Relative difference
Which is smaller: absolute or relative?
Absolute (as population increases, value continues to decrease while relative remains constant)
Probability of an outcome for an exposed or unexposed group
Risk (aka Incidence Risk)
Is risk a proportion?
YES (part over whole; new cases/tot pop exposed/unexposed)
Probability outcome for an exposed population (incidence risk in an exposed pop) EQUATION
(Those exposed/getting treatment and have disease/outcome) divided by (TOTAL population of those exposed/getting treatment) (A SIMPLE PERCENTAGE)
Probability of outcome for unexposed population (risk for non-exposed)
(Those not getting exposed/treatment but DO have disease/outcome) divided by (TOTAL population of those not exposed/getting treatment) (simple percentage)
Difference in risk outcomes that is ATTRIBUTABLE to exposure differences; useful in comparing effectiveness of treatments
Absolute Risk Reduction ARR/ Attributable Risk (AR)
Difference in risk outcomes in PROPORTION to risk if not exposed/treated; good for when discussing treatment plan (Question to keep in mind: What if you DONT take treatment)
Relative Risk Reduction
Equation for Number Needed to Treat/Number Needed to Harm
1 divided by ARR (decimal point format) (same eq!!)
