Using the American Medical Association physician masterfile to measure physician supply in small towns

The goal of this study was to describe the magnitude, direction and sources of error of the American Medical Association's (AMA) masterfile (MF) in es timating physician supply in small towns. A random sample of nonmetropolita n towns in the United States was selected, and physicians with AMA MF (MFMD s) addresses in these towns were listed. Local pharmacists were asked to co nfirm or disconfirm the identities and locations of practice for the listed physicians and to add any unlisted physicians who were there. We took phar macist confirmed or identified local source physicians (LSMDs) to be the "g old standard." The sample of 57 towns yielded 1,341 potential physician nam es. In these towns, there were 377 physicians listings only from the ME 188 only front local pharmacists, and 776 from both sources. About 80 percent of physicians identified by local informants were also listed on the MF; on ly 67 percent of physicians listed on the MF were identified by local infor mants as currently practicing in the town where they were listen. The error ill these measures declined with increasing town size. The aggregate ratio of MFMDs to LSMDs was 1.20, ranging from 1.10 to 1.28 across size classes of towns. Given the persistence of local shortages of physicians, despite a national oversupply, accurate measurement of physician supply should be a priority of rural health care planners and advocates. Although the MF is th e most comprehensive mailable national physician database reliance on it al one to make local estimates of physician supply might lead one to believe t hat there are 20 percent more physicians in small rural communities than ar e actually there. Local pharmacists can be valuable informants about rural physician availability and their in- and out-migration.