Relationships Between the Physician Density and Health Outcomes and Projections of Physician Supply and Demand in Japan

Background
The supply of physicians is one of the major health policy issues around the world. The current challenge in Japan is not only overall undersupply but the maldistribution among regions and specialties: relative insufficiencies in rural areas, and workforce shortage in hard working specialties such as surgery and obstetrics and gynecology. Current committee in Ministry of Health, Labour and Welfare, Japan focuses on the projection of national-level supply and demand through 2050, and projections among the prefectures and the specialties are not performed. Moreover, the current physician projection is based on the demand for outpatient and inpatient services, which may be dependent on physicians’ behavior. Since medical education is expensive and supported by the government, the evaluation from the perspective of health values (outcomes) that physicians are producing is also important. Therefore, the aims of this paper are: to determine the dose-response relationship between the physician density and health outcomes; and to assess the future shortage or surplus of physicians in Japan not only at the national level but prefectural level.

Methods
Assuming the health outcomes are the marginal diminishing increase (decrease) function of the physician density, the dose-response relationship was determined by using prefectural level panel data (2000-2016). I adjusted for year, sex, alcohol consumption, salt intake, smoking rate, vegetable consumption, and income level. The analysis was performed between four different physician categories and four health outcomes. The four physician categories were: physicians working in medical facilities, physicians in hospitals and clinics, cardiologists and cardiovascular surgeons, and neurologists and neurosurgeons. Four health outcomes were life expectancy, disability-free life expectancy, age-adjusted heart disease mortality, and age-adjusted cerebrovascular disease mortality. Analyses with age-adjusted mortalities were focused on corresponding specialties.
After the dose-response relationship was determined, the future supply and demand of physicians were examined in two ways: calculate the demand of physicians from the projections of life expectancies from future life tables; calculate the future life expectancies by holding the supply of physicians in each prefecture at the level in 2016.

Results
The physician density was associated with life expectancy but not with disability-free life expectancy. Age-adjusted mortalities were associated with the density of corresponding specialties. Most relationship identified were linear.
The shortage of physicians resolved as the physician density increased with time since the population declined in each prefecture. However, the time until shortage resolution varied by prefectures: more than half of them were already sufficient in 2020, while few remained insufficient even in 2040.

Conclusion
Marginal diminishing increase (decrease) was not identifiable in most of the relationships between the physician densities and health outcomes, suggesting the number of physicians in Japan is still insufficient that improvement in health outcomes by increasing physicians is expected. We need other policies to extend the disability-free life expectancy. Since the declining population increases the physician density, future restriction on admission quota for medical school is necessary. Though national-level quota should be restricted, the disparities in physician insufficiencies among prefectures indicate the policy to increase the local physicians is also necessary. The currently available evidence suggests increasing local quota with scholarships as a countermeasure. For the best of my knowledge, this is the first study to examine the future supply and demand of physicians and refining the model in the study is expected for further precise projections.