Trends in the Number of Active Physicians
Analysis of the CPS and Masterfile data indicate that the number of active physicians of all ages approximately doubled during the sample period (). In an average year, the CPS estimated 67 000 (10%) fewer active physicians than did the Masterfile during the sample period (95% CI, 57 000–78 000; P<.001). The difference between the 2 estimates was relatively stable over time and did not change significantly between the first (1979–1993) and second halves (1994–2008) of the sample (P=.38).
Trends in CPS and Masterfile Data Estimates of the Number of Active Physicians Between 1979 and 2008, in Total and by 10-Year Age Groups.
also shows the differences in the estimates by age group. Estimates from the Masterfile and CPS data were similar for physicians between the ages of 35 and 54 years, but differ markedly at both younger and older ages. Lower estimates of active physicians in the CPS were almost entirely accounted for by older physicians. On average, the CPS estimated 22 000 (20%) fewer active physicians per year aged 55 to 64 years than did the Masterfile during the sample period (95% CI, 17 000–22 000; P < .001), and estimated 35 000 (51%) fewer active physicians per year 65 years or older relative to the Masterfile (95% CI, 29 000–40 000; P<.001).
The CPS estimates indicating fewer active physicians at older ages were consistent with data on physician billing patterns available from Medicare Part B for the years 2002–2004, which indicate a sharp decrease in billing activity among older physicians. Total billing by physicians aged 65 years or older was 12% of total billing by physicians aged 45 to 54 years during 2002–2004. Similarly, in the CPS, the number of active physicians aged 65 years or older was 15% of the total number of active physicians aged 45 to 54 years during 2002–2004. However, in the Masterfile data, the number of active physicians aged 65 years or older was 39% of the total number of active physicians aged 45 to 54 years during 2002–2004, consistent with an overestimation of the activity rate of physicians in this age group.
With respect to younger physicians, the CPS on average estimated 9000 (6%) more active physicians aged 25 to 34 years than did the Masterfile during the sample period (95% CI, 4000–15 000; P<.001). The average difference between the 2 data sources increased significantly between the first and second halves of the sample (P<.001); the CPS estimated 17 000 (12%) more active physicians aged 25 to 34 years (95% CI, 13 000–22 000) than did the Masterfile during the second half of the sample.
Between the first and second halves of the sample, the average number of active physicians aged 25 to 34 years increased by 17% in the CPS data and by 4% in the Masterfile data. The 17% growth observed in the average number of first-year US residents between 1980–1993 and 1994–2007 is consistent with the CPS data and suggests that data derived from the Masterfile underestimated the growth in the number of younger physicians in recent years.
Age and Cohort Effects
shows the age effects estimated from the statistical model (jointly significant, P<.001), representing the expected number of active physicians as a cohort reaches each age range as a proportion of the number of active physicians when the cohort is aged 45 to 54 years.
Expected Number of Active Physicians When a Cohort Reaches Each Age Range as a Proportion of the Number of Active Physicians When Each Cohort Is Aged 45 to 54 Yearsa
The overall pattern of age effects is consistent with expectations of how work effort varies over the life cycle, with the largest proportion of physicians being active at the prime working ages of 35 to 44 years and 45 to 54 years. Jointly, the age effects differed significantly between the Masterfile and CPS data (P<.001), with the CPS-based age effects implying a more rapid decrease in activity at older ages. For example, relative to the number of physicians aged 45 to 54 years, data from the Masterfile estimated that 86% as many physicians will remain active between the ages of 65 to 74 years (95% CI, 83%–89%), although the CPS data estimated that only 44% as many physicians will remain active (95% CI, 41%–48%).
The age effects trace out different patterns by sex, likely reflecting the effects of childbearing female physicians. Using CPS data, compared with the peak work years of 45 to 54 years, female physicians are 59% as active at 25 to 34 years and 98% as active at 55 to 64 years. In contrast, relative to their own peak activity rates, which also come at ages 45 to 54 years, male physicians are 68% as active at 25 to 34 years, but only 83% as active at 55 to 64 years. Estimates from the Masterfile data display a similar pattern. Jointly, the estimated age effects differed significantly between men and women in both the CPS (P<.001) and Masterfile (P=.03) data, although individually the CIs on the age effect are wide in the CPS data.
shows cohort effects estimated from the statistical model (jointly significant, P
<.001), representing the expected number of physicians who will be active when each cohort reaches ages 45 to 54 years. The overall pattern mirrors trends in medical education, with little growth during the last 2 decades and increasing numbers of female physicians.9
However, estimates differed significantly between the data sources (P
<.001), with the CPS data estimating smaller cohorts than the Masterfile data for older physicians, but larger cohorts for younger physicians (because the CPS data estimate more physicians aged 25–34 years than the Masterfile data in recent years ).
Expected Number of Active Physicians for Each 10-Year Birth Cohort, Born 1905–1914 Through 1974–1983, at Ages 45 to 54 Years by Data Source and Sex
Projection of Future Physician Supply
compares the projected number and percentage change of active physicians between 2005 and 2040. Projections were constructed by using the CPS data through 2008 and the Masterfile data through 2007. Both projections allowed age and cohort effects to differ by physician sex. Compared with projections that assumed the same age effects for male and female physicians, allowing age effects to differ by sex yields a slightly larger growth in the projected workforce, reflecting that large cohorts of female physicians will soon be reaching older ages, at which time they will maintain their activity rates unlike men who have tended to work relatively less at those ages. The HRSA baseline and high-growth physician requirements scenarios1
are provided as a benchmark.
Projection of Total Number of Active Physicians Through 2040 Based on the Masterfile and CPS Data vs HRSA Estimates of Physician Requirements Through 2020a
Supply projections based on either the CPS or Masterfile data yield similar workforce growth rates between 2005 and 2020 (21.4% for the CPS data and 23.1% for the Masterfile data), reflecting 2 offsetting differences. Compared with the Masterfile data, the CPS data estimates that more physicians will exit the workforce as an increasing number of physicians reach 55 years or older, while estimating that more young physicians have been entering the workforce in recent years. Both supply projections yield growth rates close to the growth in physician requirements projected by the HRSA baseline scenario (21.7%).
However, CPS-based projections suggest that the number of active physicians will be below HRSA’s baseline requirements by 19 000 physicians in 2020, and the Masterfile-based projections suggest that the number of active physicians will exceed HRSA’s baseline requirements by 74 000 physicians—a difference between the projections of nearly 100 000 physicians (9%). This gap primarily reflects differences in how many physicians were estimated to be active in 2005, rather than differences in projected growth rates. Both projections are below the HRSA high-growth scenario, with the CPS-based projection suggesting a deficit of 155 000 physicians and the Masterfile-based projection suggesting a deficit of 62 000 physicians.
Because the CPS data result in estimates of both larger cohorts of young physicians and greater decreases in activity at older ages relative to the Masterfile data, CPS-based projections result in a younger distribution of active physicians in 2020 (). The CPS-based projection indicates that 71% of active physicians will be younger than 55 years and only 9% will be older than 65 years, whereas the Masterfile-based projection indicates that 61% of active physicians will be younger than 55 years and 18% will be older than 65 years.
Percentage of Active Physicians in Various Age Groups Based on 2020 Projections Derived From the CPS and Masterfile Data
These projections were compared with the Masterfile-based projections of physician supply constructed by HRSA (which used somewhat different methodology). To be consistent with the HRSA projection, which used data from 2000 as a base year, CPS-based and Masterfile-based projections were made using only data through 2000. Our Masterfile-based projections and the HRSA Masterfile–based projections were within 2% of each other through 2020. Both were 7% to 9% greater than the corresponding CPS-based projections and projected approximately twice as many physicians aged 65 years or older relative to CPS-based projections. This is consistent with differences in underlying data rather than methodology driving the differences between the projections.