A basic median-voter model is developed and extended to analyze issues of economic regulation and public policy outcomes. The model is used to generate comparative static results relating changes in public-policy outcomes to changes in relative group sizes, total population, information costs, and population heterogeneity. The model is also used to explore the issue of optimal group size — the size of the special-interest group that maximizes the group's per capita public policy gains. Comparative static analysis reveals how optimal group size and gains per capita are affected by changes in population heterogeneity, the size of the total population, and relative knowledge levels.