Not surprisingly, skin in the game is a good indicator of fund-manager tenure. But you may be surprised by how much.

According to a new Morningstar study, managers who have invested more than $1 million in their own funds stay twelve years, compared to less than five years for managers who have invested no money at all.  Both stock and bond funds with more manager money also had higher star ratings (although this was not a criteria in the rating system.)

Many small funds don't report any manager investment, while managers are invested heavily in some of the biggest, for example, American Funds’ Growth Fund of America, Morningstar reports.

In 2008, Russ Kinnel, Morningstar's director of mutual fund research, noticed that in the fund-rating company’s picks the fund managers were investing more of their own money. The next year, Morningstar reported that funds where managers had invested at least $1 million had much better five-year returns than those with similar investment strategies where the managers had invested no money.

In the latest study, Morningstar excluded sector funds. For a group of “core funds,” it found that the average three-year rank for funds with no manager ownership was right at the median of 50. Funds where managers invested at least $1 million ranked 38 on average, significantly better.

“It stands to reason that managers who invest in the funds they run show conviction in their strategies and are more likely to act in the long-term interests of shareholders,” according to David Kathman, a Morningstar analyst.

To find out if a fund’s manager has invested in his fund, can click on the Filings Tab for a fund to see the “Statement of Additional Information,” a SEC-disclosure document.