��Chapter 8 (Association) Exposure (E) represents the explanatory variable (e.g., smoking) Disease (D) represents the response variable (e.g., premature death) Does E lead to D? Association If the E+ group has a higher incidence of D (positive association) - E may be causal If E+ group has lower incidence (negative association) - E may be preventative If E+ jas about same incidence (no association) - no observed effect Association does not equate with causation but does provide clues Comparing Risks Suppose a 5-year risk in smokers is 2% risk & in non-smokers is 1% Absolute comparison: Risk Difference = 2%  1% = 1% Relative comparison: Relative Risk = 2% � 1% = 2 RR vs. RD RR measures strength of association (good for causal statements) RD measures excess risk in absolute terms (good for public health statements) RR & RD are related Algebraic expression Concept: a large multiplier (RR) of a small baseline risk (R_0) produces few additional cases (small RD) Multiple levels of exposure Compare each exposure level to the baseline ( non-exposed ) rate Allow for determination of dose-response relations