49. The positive correlation between health ® and income per capita is one of the best-known relations in international development. This correlation is commonly thought to reflect a causal link running from income to health…. Recently, however, another intriguing possibility has emerged: that the health-income correlation is partly explained by a causal link running the other way—from health to income” [D. E. Bloom and D. Canning, The health and wealth of nations, Science, 287 (2000): 1207–1208]. Explain how higher income in a nation can cause better health. Then explain how better health can cause higher national income. There is no simple way to determine the direction of the link.