Even after adjusting for income differences, African-American and Hispanic workers are contributing less to 401(k) retirement plans.

Hewitt Associates Inc., Lincolnshire, Ill., and an affiliate of Ariel Investments, L.L.C., Chicago, have published that finding in a summary of results from an analysis of information about 3 million workers at 57 large 401(k) plan sponsors.

Only 66% of the African-American workers studied and 65% of the Hispanic workers are participating in their employers’ defined contribution plans, compared with 77% of the white workers and 76% of the Asian workers, according to analysts at Hewitt and Ariel.

The average contribution rate is 6% of income for the African-American workers, 6.3% for the Asian workers, 7.9% for the white workers and 9.4% for the Asian workers.

The percentage of account assets invested in stocks and stock funds is 66% for the African-American workers, 70% for the Hispanic workers, 72% for the white workers and 73% for the Asian workers.

The analysts who wrote the report say one way to reduce the differences may be for policymakers to encourage employers to record information about plan participants’ race and ethnicity.