U.S. residents with health insurance and relatively high incomes are having a harder time paying medical bills.

Researchers at the Center for Studying Health System Change, Washington, have published that finding in a summary of results from a 2007 survey of 18,000 U.S. residents.

About 18% of the survey participants with health insurance reported having problems with medical bills in 2007, up from 14% in 2003, the researchers report.

Among insured participants with family incomes over 400% of the federal poverty limit, the percentage facing problems with medical bills increased to about 11%, from 7.1%.

The percentage of insured participants with medical bill problems who say they have gone without needed care due to concerns about cost increased to about 12%, from 6.6%.