Most 401(k) investors took a hands-off approach to their retirement plans last year, declining to make trades or adequately diversify their assets.

During a bear market, this is, of course, a definite plus for the mutual fund industry. While investors didn't add to their plans en masse, they didn't withdrawal large chunks of assets from them, either, said Luis Fleites, an analyst at Cerulli Associates, a Boston research firm that tracks trends in retirement investing.

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