Differences in medical schools’ regional retention of physicians by school type and year of establishment: effect of new schools built under government policy

We conducted a cross-sectional study using the Medical Database, established by a private market research company in Japan (Nihon Ultmarc Incorporated, URL: http://​www.​ultmarc.​co.​jp/​). This database contains information gathered from medical institutions and healthcare providers in Japan. The database was originally compiled by medical representatives of pharmaceutical companies, and organized by Ultmarc for use in sales and marketing by pharmaceutical and medical device companies. Medical representatives acquire information on physicians who practice in medical institutions from the institutions’ websites, and augment this information by direct inquiry and interviews with physicians. Each physician’s name and year of registration are confirmed through the website of the Ministry of Health, Labour and Welfare of Japan, which also discloses medical certification information for each physician [19]. This database is updated regularly; the version used in the study is that of May 2014. As of that date, at least 82.0 % of medical licensees were included in the database. We obtained the data in an anonymous format.

We included in our study sample physicians who had passed the National Medical Practitioners Examination between 1985 and 2013. In Japan, all medical school graduates must pass the National Medical Practitioners Examination to qualify as practicing physicians. We selected 1985 as the first year of the inclusion period because almost all of the newest medical schools began to supply graduates following this year. We excluded physicians with less than 2 years’ experience because they were junior residents and had not yet determined their specialties. We also excluded physicians whose schools were not named in the database, and those who worked in nonclinical fields, such as biomedical research or public health services. We also excluded physicians who graduated from Jichi Medical University, National Defense Medical College, and the University of Occupational and Environmental Health, because these medical schools impose practicing locations and/or specialties upon graduates as a condition of their scholarships.

We defined the primary outcome as the proportion of those physicians who practiced at clinical institutions in the prefecture of their medical school to the total number of physicians who had graduated from each school during the study period. Prefectures are municipal provinces in Japan, of which there are 47 throughout the country. The secondary outcome measure was the proportion of graduates who practiced at clinical institutions either in the prefecture of their medical school or in neighboring prefectures. These proportions are referred to as “retention rates” hereafter.

With respect to covariates, we adjusted for sex, number of years’ experience as a physician, year in which the medical school was established, whether the school was public or private, and the school’s location (whether it was located in a densely or sparsely populated city), to estimate the effects of individual and institutional factors. We categorized the number of years’ experience as a physician, in consideration of the usual career path of physicians, as follows: 3–5 years, 6–10 years, 11–20 years, and more than 20 years. We divided all Japanese medical schools into two groups: established pre-1970 or post-1970. Most medical schools established post-1970 were intended to solve physician shortages and maldistribution. Additional file 2: Table S2 lists the 46 medical schools established pre-1970, and the 31 schools established post-1970, excluding the three schools mentioned above. Medical schools were also divided according to funding source (public or private). There were 13 private schools in the pre-1970 group, and 14 private schools in the post-1970 group. In Japan, the number of students enrolled in each medical school is about 100 per year irrespective of the funding source, whereas the total tuition required is approximately 3.5 million JPY (≒US $29,160, as of October 22, 2015) for public medical schools and 20–45 million JPY (≒US $166,160–333,300, as of October 22, 2015) for private schools. The tuition burden differences between public and private schools were related to the practice settings and incomes of physicians in the United States [20]; therefore we suspected that it would be an influential factor in their choice of school and employment location subsequent to graduation in Japan. To assess the effect of medical schools located in urban areas, considered to attract physicians, we adjusted for the location of medical schools in prefectures that included cities with populations of more than 700,000.

We performed descriptive analyses of the demographic characteristics for each category. We used chi-squared tests to compare categorical variables. To perform outcome analyses, we calculated the retention rates by medical schools according to their year of establishment (pre-1970 or post-1970) and their funding source (public or private). In the multivariate analysis, we used a random-intercept hierarchical regression model with intercepts unique to each medical school, to assess the remaining school characteristics after adjusting for year of establishment, funding (public or private), and location. We did additional analyses of the secondary outcome in a similar manner. Neighboring prefectures were defined as prefectures that share borders on land.

On the basis of Ethical Guidelines for Medical and Research Involving Human Subjects in Japan, the Institutional Review Board of The University of Tokyo approved this research and determined that individual informed consent was not required (No. 10421).