Critics of American heath care—and advocates of single-payer insurance or other forms of socialized medicine—point to poor U.S. rankings in infant mortality and life expectancy. It turns out both are grossly flawed calculations that misleadingly make the U.S. rank low.

America’s rate of infant mortality—death within the first year after birth—was 5.9 per 1,000 live births in the latest statistics, 32nd among 35 developed countries, according to the Organization for Economic Cooperation and Development. But these aren’t apples-to-apples...