About 9% of U.S. adults with annual incomes between $60,000 and $99,999 may have been underinsured in 2007.

Researchers at the Commonwealth Fund, New York, have included that figure in a paper analyzing trends in the percentage of U.S. adults who appear to be underinsured.

The paper appears in the online edition of Health Affairs, a health finance academic journal.

The researchers who wrote the paper defined the term “underinsured” to include individuals who have paid 10% or more of their income for out-of-pocket medical expenses; low-income individuals who have spent more than 5% of their income on medical expenses; and individuals with health insurance deductibles that equal or exceed 5% of income.

The overall rate of underinsurance for U.S. adults ages 18 to 64 increased to 25% in 2007, from 16% in 2004, the researchers report.

The underinsured rate was 26% in 2007 for adults in the age range studied with incomes under $20,000 per year.

The underinsured rate was 13% for adults in the $40,000-$59,999 income category.

The researchers also looked at the percentage of individuals who were completely uninsured.

In the $40,000-$59,999 category, for example, 18% of the individuals were uninsured at some point in 2007, meaning that those individuals were more likely to be completely uninsured than to be underinsured.

In the $60,000-$99,999 category, the situation was different. In that category, 9% of the individuals were underinsured, and 9% were uninsured at some point in 2007.

In 2003, only 4% of the individuals in that income category were underinsured, and only 6% spent any time completely uninsured.

For individuals earning more than $100,000 per year, the underinsured rate climbed to 7% in 2007, from 1% in 2003. The uninsured rate rose to 6%, from 2%.

When policymakers increase deductibles in an effort to lower premiums, the “trade-offs may weaken support for mandates or raise care concerns, especially for preventive services and chronic care,” the researchers write.