A new study finds that 49 percent of U.S. workers in small businesses were offered health insurance in 2010, down from 58 percent in 2003.

Firms with 100 or more employees were far more likely to provide health benefits, at 90 percent in both 2003 and 2010, according to the report from the Commonwealth Fund, a foundation that does health care research.

Low-wage workers in small businesses were the least likely to be offered coverage: One-third of workers making less than $15 an hour in small firms were able to enroll in their employer’s health plan.