Requiring U.S. employers to provide health insurance to most employees working at least 20 hours a week might not be the best way to achieve universal coverage, according to research by the Federal Reserve Bank of San Francisco.

In Hawaii, where such a mandate was enacted in 1974, businesses have relied more on employees who work less than 20 hours per week and aren't covered under the state requirement, wrote San Francisco Fed research adviser Rob Valletta and co-authors Tom Buchmueller and John DiNardo, both University of Michigan professors.

“;The results of our research”; into health insurance coverage in Hawaii “;imply that an employer mandate is not an effective means for achieving universal coverage. Although overall insurance coverage rates are unusually high in Hawaii, a substantial number of people remain uninsured, suggesting a need for alternative approaches if universal coverage is the ultimate goal,”; they said.

Legislative proposals in both chambers of Congress would expand health insurance coverage to 46 million Americans who are uninsured in part by requiring businesses to provide coverage or pay subsidies for such a benefit. President Barack Obama has left Congress the task of crafting universal health care while saying he wants to sign such a measure by October.

The percentage of Americans receiving insurance through their employer or that of a family member's has dropped to 59 percent in 2007 from 64 percent in 2000, according to the Fed paper released yesterday.

The focus on health care is unusual because previous papers from the San Francisco Fed have focused on the economy or monetary policy.