Equitable distribution of physicians is a key component of access to health care [1, 2]. Prior studies have focused on its social and demographic determinants, including household income [3–5], education , population density , and racial composition . In addition, some researchers have noted different preferences of physicians for locating urban versus rural areas [5, 9, 10].
However, earlier studies have at least two knowledge gaps that should be addressed comprehensively. First, the vast majority of analytic studies on physician distribution were based on data derived from developed nations. Whether their findings could be generalized to developing countries, such as China, is unknown, since the financing, healthcare delivery, and social contexts differ substantially between developing and developed nations. At the same time, China’s experience may provide useful lessons to not only other low and middle-income nations but also high-income nations [11, 12].
Second, current research has focused on the disparities in physician distribution between urban and rural areas, with limited attention to the heterogeneity across cities . This is an important gap, particularly in China, as Anand et al. (2008) noted that, in urban areas, where more than half of Chinese resided, the inequality in the distributions in physicians and nurses was twice as high as that in the rural areas . Since the market reform in 1978, an estimated 262 million people have migrated from rural areas to urban areas because of greater job opportunities, better social welfare, and improved living conditions [15, 16]. However, prior studies did not examine how cities' attributes were associated with physician distribution in China.
Cities in China can be divided into three categories: provincial-level cities, prefecture-level cities, and county-level cities, reflecting the substantial heterogeneity in economic development, population density, and social welfare . Also, they are hierarchical because provincial/prefecture-level cities encapsulate densely populated urban districts as well as sparsely-populated county-level cities and counties. Urban districts have been traditionally recognized as the narrowly-defined provincial/prefectural-level cities since social welfare in urban districts is better than county-level cities and counties [17, 18].
Furthermore, there exist significant economic disparities across regions in China. Regions close to coastlines, where the market-oriented reform was first initiated, such as the Eastern Region, are economically more developed relative to other regions .Thus, Eastern China is recognized as more attractive to physicians in comparison with Western China, which has experienced significant brain drain .
As a vehicle of its economic development strategy, China has established a number of urban agglomerations (U.A.s). An U.A. or city cluster consists of several metropolis or large cities, which form a multi-layer group centered on one or two most prosperous cities . Representing a more advanced form of urbanization, each U.A. has its dominant industries, connected transportation networks, and similar social public welfare . Geographic information of regions and U.A.s is presented in Supplemental Materials Fig. 1.
Objectives And Hypotheses
This research aims to analyze China’s urban disparities, i.e., urban districts vs. county-level cities, in physician density with particular interests in the roles of regions and U.A.s in 2003 and 2013. We conceptualized the differences in physician distribution as a function of population and socioeconomic attributes, which significantly affected the supply and demand for physician services. As a guide for data analysis and interpretation of findings, we offered four hypotheses.
First, equality in physician density across cities in China improved significantly between 2003 and 2013 (H1), given the significant growth of human healthcare resources  and substantial economic growth . However, the improvement might vary as a function of demand and supply of physician services as reflected by demographic and socioeconomic characteristics across cities and their changes over time (H1a).
Second, physician density is higher in urban districts than county-level cities, even when demographic and socioeconomic characteristics are controlled (H2). Disparities in physician distribution across cities are largely driven by the uneven distribution of supply factors that affect physicians' location choices, including opportunities for education, professional prestige, and physician origin . In addition, population growth, particularly population aging, and economic development lead to increased demand for physician services .
Third, the urban disparities in physician distribution may exacerbate across regions (H3) as there are substantial regional differences in socioeconomic development because of structural and long-term factors including education, regional labor supply, and geographic location . For instance, the national government adopted preferential policies such as the Open and Reform, benefiting the coastal area disproportionally, and the Western Development policy, creating favorable conditions for investment in Western provinces .
Fourth, recent initiatives of creating urban agglomerations across China to promote economic growth is associated with increased physician density (H4). China's government has invested substantial resources in new industrial parks to generate spillovers for the local economy. There is some evidence of the geographic spillover effect of parks as an increasing function of overall human capital level, foreign direct investment share, and its "synergy" with nearby incumbent firms .