The theoretical model gives a sharp prediction – retention of NHSC participants in HPSAs after the completion of their obligations can never be higher than the retention of providers who choose to locate in those areas without participating in the program. In the limiting case where selection into the program is based solely on preferences, the program selects individuals who would have tended to serve in high-need areas in the absence of the program and retention differences between participants and non-participants are nil. As the correlation between location preferences and program fit weakens, the program tends to select individuals who would not have gone to high-need areas in the absence of the program. In this case, participant retention after program completion will tend to be lower than non-participant retention. Somewhat counterintuitively, a lower retention rate for non-participants is a signal of the program’s success in attracting to high-need areas providers who would not have located there in the absence of the program.