Simple between-group comparisons of category representation percentages can be misleading for investigation of differential group selection procedures—the presence of a strong selection factor can obscure the effects of intermediate factors. This paradoxical effect is easily resolved through elementary application of the Bayes theorem. Because category representation percentages are often convenient and intuitively appealing to the statistically naive, however, there exist diverse and pervasive opportunities for incorrect interpretation with fallacious conclusions. Toxic shock syndrome epidemiological data are used to illustrate the paradox.