PubMed · 5617299
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I J Bravo. [Demography and development].. https://pubmed.ncbi.nlm.nih.gov/5617299/
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Physician supply and demand for the period extending to 2020 were assessed from three perspectives: physician utilization in group- and staff-model health maintenance organizations, physician distribution, and the future supply of nonphysician clinicians. The national norm for physician demand in 1993 was estimated to be 205 per 100,000 population. Demand is projected to increase 18% by 2020, because of both an expansion in beneficial services and a reduction in physician work effort. Supply initially will increase more rapidly, resulting in a surplus of 31,000 physicians (5% of patient care physicians) in the year 2000 and increasing to 62,000 physicians (8%) in 2010, after which the gap will narrow. Similar results were obtained when previous studies that had projected surpluses of 73,000 to 165,000 physicians (15% to 30%) in the year 2000 were reevaluated. However, physician distribution is not homogeneous, and the number of physicians per capita currently varies by more than twofold among states. Relative to the national norm, surpluses already exist in some states and shortages in others. In addition, the supply of nonphysician clinicians with independent practice authority is increasing. Their numbers are projected to double by 2010, equaling 60% of the number of patient care physicians. Measured as physician equivalents, their growth will equal the growth in physician supply. Thus, in terms of physicians alone, there is no evidence of a major impending national surplus. Local surpluses will be influenced principally by how physicians distribute themselves geographically. The major determinant of overall physician surpluses in the future will be the extent to which patients continue to seek physicians for services that also will be offered by an expanded workforce of nonphysician clinicians. Policy is needed that encompasses the universe of clinicians who will be providing care to patients in the next century.
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A new model is presented for the genetic structure among a collection of island populations, with fluctuating population sizes and continuous overlapping generations, using a stochastic birth, death and immigration (BDI) process. Immigrants enter each island from a large mainland population, with constant gene frequencies, according to a Poisson process. The average probability of identity by descent (IBD) for two haploid individuals randomly selected from an island population is f0 = (phi f1 + lambda)/(phi + lambda), where f1 is the probability of IBD for two randomly selected immigrants, lambda is the birth-rate for each individual, and phi is the arrival rate of immigrants into each island. The value of f0 is independent of the death process, time and N. The expected level of genetic differentiation among island populations is FST = (1 - 1/n)lambda/(phi + lambda), where n is the total number of islands receiving immigrants. Because f0 and FST are independent of the death process, for a BDI model, the population genetic structure for several general demographic situations may be examined using our equations. These include stochastic exponential, or logistic (regulated by death rate) growth within islands, or a ""source-sink" population structure. Because the expected values of both f0 and FST are independent of time, these are achieved immediately, for a BDI model, with no need to assume the island populations are at genetic equilibrium.