For each 10 percentile increase in the primary care physician supply at the county level, the odds of late-stage diagnosis decreased by 5%, with a comparable increase with each 10 percentile increase in specialty physician supply. The effect is greater in urban areas than in non-urban areas. It was also greater in higher socioeconomic areas than in lower ones, perhaps due to poorer access to existing primary care services in areas of lower socioeconomic status.

Source: Roetzheim RG, Pal N, Gonzalez EC, Ferrante JM, Van Durme DJ, Ayanian JZ, et al. The effects of physician supply on the early detection of colorectal cancer. J Fam Pract 1999; 48(11):850-858.