A relative shortage of physicians in rural areas has been reported over the last few decades in Japan [1–5]. In the 1970s, the Japanese government introduced the policy of establishing at least one medical school per prefecture and increasing the total number of medical students. By the mid-1980s, the number of medical graduates, or newly certified physicians, per year had doubled from about 4000 to 8000. In 1984, the Ministry of Health and Welfare (now the Ministry of Health, Labour and Welfare and hereafter MHLW) announced that the targeted ratio of physicians per population had been achieved. As a result, beginning in 1985, medical school admissions were reduced to prevent a future oversupply of physicians. In 1993, the numbers of those entering medical schools fell to 7725, or 7.7% fewer than in 1984. Since the target reduction was 10% from the number admitted in 1984, the cutback in entering medical students continued. In 1997, a cabinet meeting approved this further reduction. In 2007, 7625 students were accepted for medical training, or 92% of the 1982 entering class.
However, by 2007, a relative shortage of physicians in Japan became evident. In that year, the number of physicians per 1,000 population was 2.1, while the number of medical graduates per population of 100,000 was 6.0, ratios that placed the nation in the 26th and 28th positions respectively among the 30 Organisation for Economic Co-operation and Development (OECD) countries . On May 31, 2007, the Japanese government announced the "Active Plan for urgent supply of physician." From 2007 to 2008, the Ministry of Education, Culture, Sports, Science and Technology, increased medical school admissions for the first time in twenty-eight years, permitting 7793 students to begin their training. The increase in new medical students continued, and by 2009, their numbers reached 8,486, exceeding the peak of the early 1980's. In 2010, 8,846 were admitted, a 16% increase from the low point at the beginning of the century.
Previous studies of this increase in medical students on the distribution of physicians in Japan reveal that while the absolute shortage of physicians lessened, their geographical maldistribution persisted [1, 4, 5]. Furthermore, since 2004, MHLW has implemented mandatory two-year post-graduate training in designated clinical training hospitals for all newly certified physicians. Inequalities in physician distribution may have widened after the implementation of this mandatory system, since most clinical training facilities are either university hospitals or those certified for training by the MHLW, and both types are typically located in urban areas. However, few studies exist on the impact of the new post-graduate training system on physician distribution in Japan .
To analyze disparities in the allocation of physicians, the number of physicians per population at the municipality or county level is commonly used [1, 3–5, 7, 8]. However, a number of published analyses suggest that this indicator is not necessarily useful or revealing at the municipality level in Japan, for while the populations of municipalities vary by an order of magnitude of 5000 in Japan , it assumes that residents only seek care in their own county and ignore patient flows into adjacent areas [8, 10, 11]. The proportion of municipalities with small populations is high in Japan. In 1999, 1531 (45.5%) of 3368 municipalities in the nation contained fewer than 10,000 people. After a massive merger of municipalities undertaken between 1998 and 2006, the total number of municipalities decreased, as did the proportion of those with small populations. By 2009, Japan had 1926 municipalities of which 489 (25.4%) had populations smaller than 10,000. Because of the high proportion of small municipalities, the percentage of these with small numbers of practicing physicians is high. Surveys of physicians, dentists, and pharmacists conducted by the MHLW in 1998 indicated that 1711 of 3371 municipalities (50.8%) had nine or fewer practicing physicians. After the period of municipal mergers between 1998 and 2006, 557 of 1951 municipalities (29.6%) had nine or fewer practicing physicians in 2008.
This finding indicates that many municipalities might be too small to maintain medical facilities employing multiple physicians. In other words, examining medical resource allocation at the municipal level does not necessarily yield insightful information. Consequently, in analyzing physician allocation disparities, it is best to define a region as an entity whose population is larger than those of counties and municipalities and smaller than those of states, provinces, and prefectures. In dealing with large states, this approach assumes that the physician per population ratio is uniform throughout the state, even if persons living in areas adjacent to metropolitan counties are more likely to seek care in the latter [8, 12–17].
The 1985 revisions to the Medical Service Law (here after the Medical Service Law) directed each prefecture to establish a system of regional medical services, in order to provide efficient and appropriate medical care with finite resources and to improve collaboration between medical, community health, and social welfare service providers. The primary tier of medical care is mainly concerned with primary care and ordinary outpatient care. The Medical Service Law contains no specific regulations for the spatial unit of this primary tier. However, in most prefectures, the municipality is its spatial unit. The secondary tier of medical care (STM) is mainly concerned with most admissions and surgical, emergency, and ambulatory services. Usually, a prefecture is divided into five to ten STMs on the basis of its medical resources, transportation, and geographical situation. Most of the STMs are based on a complex of adjacent municipalities. Therefore, the STM is concerned with primary care, ordinary and specific outpatient care, and usual inpatient care. "Initial, secondary and tertiary emergency medical services" are all contained within a STM. Inflows and outflows of patients are very limited in a STM, except for specific and advanced treatment of certain special conditions. According to the Patient Survey , 76% of the hospitalized patients lived in the same STM of the hospital in 2008. The tertiary tier of medical care provides medical services for an area that cannot readily be met by the primary and secondary tiers, such as the treatments performed at a university hospital.
After 1950, although annual population growth rate was positive in the urban areas of developed countries, including Japan, it was negative in rural ones . Local population decline and the inflow of people to urban areas continue. In considering the number of the physicians per population, we must examine the change of both population and the number of the physicians at the same time because urbanization widens the disparity between the rural area and urban areas. Particularly in areas with a small number of inhabitants, the number of the physicians per population increases when the percentage of population decline exceeds that of physician decrease. In this case, it may be difficult to maintain the function of medical facilities, such as hospitals, because the number of the physicians actually falls.
As mentioned above, the STM is an area established by the Medical Service Law and related legislation. However, few inquiries into the allocation of medical resources at the STM level have been carried out [20, 21]. In the study presented here, we examine three hypotheses. First, the increase in the number of physicians between 1998 and 2008 did not lead to a more equal distribution of physicians. Second, during the same period, the maldistribution of population escalated. Third, despite the decrease in the number of practicing physicians in STMs with smaller numbers of inhabitants, the fall in the denominator populations caused an increase in the former per population.