Approximately 37% of investors are participating in target-date funds when their employer offers one, according to the Employee Benefit Research Institute.

That percentage is likely to grow as more employers automatically enroll new employees into these plans, EBRI said. Target-date funds held about 7% of total 401(k) plan assets in 2007.

"Younger workers are significantly more likely to invest in target-date funds than older workers," the study said, noting that "almost 44% of participants under age 30 had assets in a target-date fund, compared with 27% of those 60 or older."

Most investors in target-date funds have low incomes, few assets and little time on the job.

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