A measure of association quantifies the relationship between exposure (i.e. risk factor) and outcome (i.e. mortality or morbidity).  This is necessary in ascertainment of causes and effect and to test hypothesis about causal relationships.

Examples of commonly used measures association include risk ratio (relative risk), odds ratio, rate ratio, and proportionate mortality ratio. In this introductory module we cover the most commonly reported measures, relative risk and odds ratio.

Figure 1. How to present your study information in a 2X2 Table

To calculate Relative Risk (RR) and Odds Ratio (OR):

–        RR=(A/(A+B))/(C/(C+D))

–        OR= (A*D)/(C*B)