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This is sure to make financial advisers cringe, or at least send me a few angry emails. German researchers have found that on the whole, investors who use a financial adviser tend to underperform do-it-yourselfers.

Professors from Goethe University Frankfurt gathered data from a large German brokerage firm that allowed its clients to either run their portfolios themselves or use an independent financial adviser. On the whole, the adviser-led clients did better. But the researchers found that clients with advisers tended to be older and wealthier than average. Once the professors controlled for age and wealth, they found that the clients with advisers did worse.

The professors write, "Advisors actually tend to lower returns, raise portfolio risk, increase the probabilities of losses, and increase trading frequency and portfolio turnover relative to what account owners of given characteristics tend to achieve on their own."

Yes, there could be something unique about the brokerage that they studied. Or maybe German advisers happen to be particularly dense. But I'm more inclined to think that the advisers in the study suffered from the same biases that often make lay people such poor investors. They chased hot stocks and dumped ones that cooled off. Because they thought their job was to outperform the market, they felt a compulsion to do something -- anything -- when the right move was to stay put. Sprinkle fees and commissions on top -- some of which reward advisers for being active traders -- and the advisers didn't really stand a chance.

What could the brokerage clients have done to avoid getting screwed over? For one, they could hire planners who charge only fees, not commissions, and earn the same whether they make one trade a year or 100. They could also make sure the adviser espouses a passive, low-turnover strategy that focuses on keeping costs down rather than trying to beat the market.

But the study's also a reminder: You can't just outsource your finances. It's your future at stake, and you'd better look over your adviser's shoulder.