Fig. 4. Log new case incidence of AIDS, tuberculosis, and violent crime in New York City plotted against the composite index for commuting and poverty. Mu/Area is the county index of commuting density (see Wallace et al. 1997) and Perpov is the percentage of a county’s population that is in poverty. Each data point represents one of the 24 counties of the New York City Metropolitan Region, including the five boroughs. These regressions are parallel, as indicated by analysis of covariance.