Health savings account programs seem to be most popular with workers at small employers and with lower-income workers.

Researchers at UnitedHealthcare, a unit of UnitedHealth Group Inc., Minnetonka, Minn., have based those figures on an analysis of information on about 200,000 of the 1.4 million plan members in HSA-eligible plans in 2006, the latest year for which full-year figures were available when the analysis was conducted.

Participation rates were highest at small businesses and the lowest-income groups, the researchers report.

The participation rate was 74% at companies with 1 to 99 workers, and 64% for individuals with annual incomes under $25,000.

About 68% of the participants contributed their own money to the HSAs, 88% had a balance at the end of the year, and participants who carried a balance had an average of about $900 in the accounts, the researchers report.

About 86% of the eligible employees opened an HSA when the employer contributed anything to the HSA, and only 27% opened an HSA when the employer contributed nothing, the researchers report.