Fig. 1. Hypothesized benefit of using the intersect, at a SNP associated with ischemic stroke.

Circles indicate the non-risk allele, and crosses the risk allele. Using a chi-square test (visualized with contingency tables), the measured effect is stronger with a group of cases that is more homogeneous but smaller (intersect, purple) than with a group of cases that is less strictly defined but is larger (union, teal).