Health care costs are unaffordable for 25 percent of working-age adults with private insurance coverage, according to the new Commonwealth Fund Health Care Affordability Index. Released in the issue brief How High Is America’s Health Care Cost Burden?, the index measures premiums, deductibles, and out-of-pocket spending as a share of income. It is based on a survey of privately insured adults, 90 percent enrolled in employer plans and 10 percent in marketplace plans or individual coverage.