You're invested in a well-performing mutual fund. The highly regarded fund manager appears to be at the top of his game. Everything is going great.

Then the manager announces he is retiring, or perhaps leaving for greener pastures. Should you sell that fund?

Selling when a management change occurs is a common investor practice — often egged on by speculative reports in the financial media. But new research from Morningstar — reported in The Wall Street Journal — has found that, on average, "there is no change in a fund's future performance after a management change."

And it's not just that there is no performance change within the next few weeks or months after new management takes over. "Morningstar considered results up to two years after a change was made. But no matter how it looked at the data, there was, on average, no change in performance."

Morningstar analyst Madison Sargis attributes this remarkable lack of impact to that fact that 75% of U.S. stock and bond funds are now managed by teams. Even among funds with a single manager, most such managers are "supported by a research staff with strict processes and restrictions on investments that fit within their mandate."

The Morningstar research piles up more evidence against the idea that certain "hot hand" managers are uniquely gifted and are able to do what others can't.

That said, we at SMI have long considered some managers to be more skilled than others, and we're happy to note some of a manager's background or history when one of our Upgrading recommendations warrants it. But we don't base our recommendations on who is managing a particular fund. Instead, we focus exclusively on fund performance as quantified by our momentum calculations.

Performance is the telltale indicator, not the name(s) in the fund-manager box. If a fund on our recommended list undergoes a management change, we hardly give it a second thought. In all likelihood, a fund with solid momentum will continue to perform fine for a while longer. Eventually, as market conditions change, the fund's momentum will begin to wane — just as it would have with the original manager.

When that happens, then it's time to sell.