When it comes to managing your retirement account, how much better off are you with getting the services of a professional? And what was the biggest investment mistake most go-it-alone types made in the last five years? A nationwide study appears to answer both questions.

Keeping in mind that the study was conducted partly by financial adviser Financial Engines, it appears that you’re better off getting professional advice rather than picking investments on your own: 401(k) account holders who used a finance pro reaped 3% more than those who picked their own investments. That’s the verdict from an analysis of investors covering the period 2006 to 2010.

The study defined “professional help” as a wide range of assistance, including use of target-date mutual funds, a professionally managed account or accessing online advice. The scope of the study covered about 425,000 401(k) accounts.

Researchers in the study pointed to one major mistake that go-it-alone types made that dragged down their returns: jumping out of the stock market when securities tanked in 2008 and then not getting back in for the run-up in 2009. Most financial planners at the time advised their clients to ride out the downturn and stay in the market.

If you apply the 3% difference to an initial investment of $10,000 over a period of 20 years, the account holders who got help would have $71,400; the ones who handled their own would have $42,100.

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