Provider Retention in High Need Areas. Marginal Effects

12/22/2014

The coefficients in Tables V.1-V.4 are logit coefficients and hence do not provide a direct indication of the magnitude of the effect of various characteristics on the average retention probability of providers in HPSAs.  It is therefore useful to calculate marginal effects, which show the ‘ceteris paribus’ differences in retention probability (measured in percentages point) relative to the mean retention probability.  In Figure V.1 we present the marginal effects associated with NHSC participation for primary care HPSAs (‘same HPSA’ and ‘any HPSA’, respectively).

Figure V. 1: Differences in the Participants’ Retention Probability Relative to Non Participants – Primary Care

Differences in the Participants’ Retention Probability Relative to Non Participants – Primary Care

In the first year since separation/start year, NHSC participants are 37.0% less likely to remain in the same HPSA relative to non-participants.  This difference represents a regression-adjusted difference, obtained by netting out the impact of other (observable) individual socio-demographic and local area characteristics.  Given that the unadjusted difference in the retention rate in the same HPSA in the first separation/start year is 42.8 percentage points (=83.5-40.7, from Figure VI.1), it follows that 86.4% (=37/42.8) of the observed difference in primary care ‘same HPSA’ retention is explained by NHSC participation.  A similar fraction, 85.6% (=13.7/16.0), in the observed retention difference was explained by NHSC participation in the case of primary care ‘any HPSA’ in the first separation/start year.  The other ratios between adjusted and unadjusted retention differences in retention between participants and non-participants remained about the same for the other further out separation/start years, for both primary care ‘same HPSA’ and ‘any HPSA’ measures.

Figure V.2 presents the regression-adjusted retention differentials by NHSC participation for mental health HPSAs.  The retention differentials are lower across the board for the ‘same HPSA’ measure than in the case of primary care HPSAs.  For the ‘any HPSA’ measure the differences in retention between participants and non-participants were practically zero, as shown by the statistically insignificant coefficients in Table V.2.

Figure V. 2:  Differences in the Participants’ Retention Probability Relative to Non Participants—Mental Health

Differences in the Participants’ Retention Probability Relative to Non Participants—Mental Health

As shown in Figure V.1, the unadjusted retention in ‘any HPSA’ was higher for non-participants in the first separation/start years than that of participants.  Nonetheless, after accounting for individual-level and local area characteristics, there was no statistically significant difference between the retention of participants and non-participants in mental health HPSAs for in any of the separation/start years.

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