The cost of long-term mutual funds continues to decrease for participants in 401(k) plans, according to a study by the Investment Company Institute released Monday.

The decline reported in The Economics of Providing 401(k) Plans: Services, Fees and Expenses, 2013, which showed a decline last year over 2012, is consistent with the downward trend that has occurred during the past decade, says ICI, the Washington, D.C.-based national association of investment companies 

At year-end 2013, nearly 38 percent of 401(k) plan assets were invested in equity mutual funds. In 2013, 401(k) plan participants who invested in equity mutual funds paid an average expense ratio of 58 basis points, down from 63 basis points in 2012, the report says.

Similarly, expense ratios that 401(k) plan participants paid for investing in hybrid mutual funds fell from 60 basis points in 2012 to 58 basis points last year. The average expense ratio that 401(k) plan participants paid for investing in bond mutual funds dropped from 50 basis points in 2012 to 48 basis points in 2013, ICI says.

“It is clear from this study that 401(k) participants investing in mutual funds tend to invest in lower-cost funds,” says Sean Collins, senior director of industry and financial analysis. “This tendency on the part of investors sets up a competitive dynamic within the fund industry, as funds strive to provide ever better services at even more competitive prices.”