We all know that the rates of uninsurance are creeping up year after year, but so are rates of "underinsurance." That means that more people who actually have coverage aren't adequately protected from high out-of-pocket medical expenses. A new study from the Commonwealth Fund has all the details. How do they define underinsurance? "Respondents were identified as underinsured if they spent 10 percent of more of their income (or 5 percent if they were low-income) on out-of-pocket medical expenses, or if they had deductibles that equaled 5 percent or more of their income." The latter criterion would mean that a great many people with high-deductible plans (including those with HSAs) meet the Commonwealth Fund's definition of "underinsured." By these measures, 14% of nonelderly adults were underinsured in 2007. Add that to the number who lacked insurance coverage at some point during the year, and you have a stunning figure: 42% of American adults were uninsured or underinsured in 2007.