income = 0.549; low income = 0.595). These ratios were derived by WHO from the current (2013) ratios of nurses and midwives to physicians and multipliers for all other workers (WHO 2016).

# **Results**

Table 1 summarizes the estimated coefficients from the demand model. The income elasticity for physicians per capita is 0.23, which indicates that a 10 percent increase in per capita GDP (lagged 1 year) is correlated with a 2.3 percent increase in physician density. The elasticity of physician density with respect to OOP health expenditures is negative (consistent with our hypothesis) and significant, indicating that a 10 percent increase in OOP expenditures (lagged 2 years) is associated with a 1.0 percent decrease in physician density. In addition, a 10 percent increase in the size of the population aged 65 or older (lagged 3 years) increases physician density by 5.2 percent.

Table 2 presents projected health worker demand, supply, and differences (supply – demand) for 2013 and 2030. The difference between the number demanded and the number supplied is then shown as either shortage (negative) or surplus (positive). These data projections for each country are further stratified according to resulting overall shortage or surplus of health workers (again defined as the difference in supply and demand) and are shown in Tables 3 and 4, respectively, for 2013 and 2030.

Table 2 shows that by 2030, worldwide demand for health workers will increase to 80 million, but only 65 million will be supplied, amounting to a shortage of some 15 million workers. This is over a two‐fold increase over the estimated shortage of 7 million workers in 2013. In 2030, the largest shortages are predicted to occur in the East Asia and Pacific (8.3 million), followed by South Asia (3.2 million), Latin America and Caribbean (2.6 million), and Europe and Central Asia (1.2 million). In terms of income groups, the highest level of shortages in 2030 will occur in upper middle income countries, followed by lower‐middle income countries. These countries are likely to experience relatively higher rates of economic growth and population aging, which will generate substantial demand for health workers that may not be adequately met by the increase in supply of health workers. In contrast, countries in Sub‐Saharan Africa region show a surplus of health worker (0.8 million), indicating that these countries may experience unemployment or under‐employment of health workers. Paradoxically, as will be discussed below, this labor surplus in Sub‐Saharan Africa will occur in the context where the demand and supply of health workers remain significantly below the WHO SDG threshold of 4.45 workers per 1,000 population needed to achieve UHC.

Table 3 shows that in 2013, 68 countries showed an aggregate shortage of 11.6 million health workers, while 97 countries showed a surplus of 5.0 million. Table 4 shows that by 2030, some 87 countries will experience health worker shortages of 19.3 million, while the surplus of health workers will reduce to 3.8 million workers across 78 countries. The substantial portion of countries exhibiting a surplus of health workers in 2030 suggests that such excesses of workers 9