Every method for computing the need for Primary Care Physicians in Alabama must start by defining a collection of service areas that partition the state. The assumption is that patients in a service area will seek care from a PCP in that service area. The service areas could possible be
Counties are most commonly used, but are perhaps too coarse. ZIP code areas and census tracts are too fine. All of the first three are artificial, based on boundaries that have nothing to do with healthcare. PCSAs are the most rational and have the proper resolution. The various area layers can be viewed in the interactive map.
After defining service areas, the next step is a computational model for determining the number of (full-time equivalent) PCPs needed for the service area, and then comparing that with the number of PCPs present in the service area. The models are complicated by the fact that pediatricians generally only serve patients in the 0–19 age group, while internal medicine physicians generally only serve patients in the 20+ age group. Family medicine physicians, on the other hand, serve patients in all age groups. For the remainder of this discussion, the term PCP refers to a full-time equivalent primary care physician.
The most common model for determining need is based on computing population to PCP ratio or PCP to population ratio in the service area. The distinction between pediatricians, internal medicine physicians, and family medicine physicians is usually ignored, so that all PCPs and all patient age groups are combined. The various ratio methods are equivalent. In this presentation, we use the number of PCPs per 10,000 population so that the numbers are smaller and easier to understand. So for example, the need could be based on a desired PCP per 10K ratio of
Another method is to compute the demand for PCP services, based on the demographics of the service area, and the supply of PCP services, based on the number of PCPs in the service area. Both supply and demand can be based on time or visits (or perhaps other metrics). We use visits in this presentation. Supply and demand models have the further benefit of allowing the distinction between pediatricians, internal medicine physicians, and family medicine physicians to be taken into account.
The following table gives the mean and the standard error of the number of visits per year (VPY) to a primary care physician (PCP) for various age groups. The data are from the National Ambulatory Medical Care Survey, published by the Centers for Disease Control.
| Age | Mean VPY | Standard Error VPY |
|---|
On the other hand, on average, according to the 2018 Survey of America's Physcians by The Physicians Foundation, an FTE PCP sees on average 20 patients per day. We also assume that an FTE PCP works 5 days per week, for 48 weeks per year, for a total of 4800 visits year. This is the supply in visits per year per FTE.
The total average number of PCP visits needed per year for the age group 0–19 can be computed by multiplying the population in each age group (0–4, 5–9, 10–14, 15–19) by the mean visits per year for that age group, and then summing over the four age groups. This gives the demand for the service area in visits per year for the 0–19 age group. Dividing by 4800 gives the number of PCPs required for this age group in the service area. Since pediatricians only see patients in this age group, the difference between the number of pediatiricans in the service area and the number of PCPs required is the surplus (if positive) or deficiency (if negative). The deficiency, if there is one, could be made up with additional pediatiricans or FMs.
Similarly, the total average number of PCP visits needed per year for the age group 20+ can be computed by multiplying the population in each age group (20–24, 25–34, 35–44, 45–54, 55–59, 60–64, 65–74, 75–84, 85+) by the mean visits per year for that age group, and then summing over the nine age groups. This gives the demand for the service area in visits per year for the 20+ age group. Dividing by 4800 gives the number of PCPs required for this age group in the service area. Since internal medicine only see patients in this age group, the difference between the number of IMs in the service area and the number of PCPs required is the surplus (if positive) or deficiency (if negative). The deficiency, if there is one, could be made up with additional IMs or FMs
To arrive at a single estimate for the FM surplus or deficiency in a service area, we first combine the PCP deficiency for the 0–19 age group with the PCP deficiency for the 20+ age group. The difference between the number of FMs in the service area and the total PCP deficiency is our estimate. Note that a surplus of pediatricians in a service area (if there is one) plays no role since pediatricians do not serve patients in the 20+ age group. Similarly, a surplus of IMs in a service area (if there is one) plays no role since internal medicine physicians do not ordinarily serve patients in the 0–19 age group.