The percentage of workers ages 21 to 64 participating in a 401(k)-type retirement plan was 33% in 2005, up from 24% in 1996, the Employee Benefits Research Institute reports.

Among workers with family incomes below $10,000, 7.4% took part in a defined-contribution plan in 2005, compared with 45% of those with family incomes of $75,000 or more.

Participation also improved with education, ranging from 11% of workers without a high school diploma to 50% of those with a graduate degree, EBRI, Washington, says.

White workers’ participation rate was 37%, followed by “other” (32%), black (27%) and Hispanic (19%).

Average annual contributions for workers ages 21-64 paying into such plans rose from about $3,728 in 1996 to $4,274 in 2005, in 2005 dollars. Men and women participated at about the same rate in 2005, roughly 33% each, but men’s average contribution was $4,949, and women’s was $3,540.