(MONEY Magazine) – More companies are giving employees access to their 401(k) plans over the Internet. But how does such a change affect investment behavior? A recent study by Metrick--along with Harvard Associate Professor David Laibson and Harvard grad student James Choi--of 100,000 retirement plan participants at two large companies indicates that Web access leads to a big increase in trading.

Q. What did your research reveal?

A. The average participant in the 401(k) plans we studied traded more, both in terms of the number of trades they made and the portion of their portfolio they made changes to. By the end of the sample period, they were trading on average about twice as much as before. So that's the fact. The question is, of course, what does it mean. That is less clear. There are some who want to interpret the results and say people are being very speculative and they're frittering away their 401(k) plan. I don't see evidence for that.

Q. Why not?

A. We are looking at the data carefully to see if speculative trading has gone up. We decided to define a speculative trade as one that gets reversed within five days or one that's placed between three and five in the afternoon, kind of waiting until the end of the day to see what to do. By these measures, speculation hasn't increased.

Q. But how has the increased activity affected portfolio performance?

A. We're not finding any evidence that performance has gone up or down due to increased trading. I just don't think there's any evidence yet that people's trading more in their 401(k) plans is bad for them. In fact, I would almost say, to the extent that people are going to trade a lot anywhere, let them do it in their 401(k)s. Let them do it where they don't have to pay taxes or transaction costs.

Q. But haven't we always heard that heavy trading impairs performance, even in retirement accounts?

A. I think that is the wrong conclusion here. I think the jury is absolutely still out on this. Trading goes up, yes, but there's no evidence to suggest that people are frittering away their savings. Now somebody is bearing the cost of this increased trading, and that may be the companies, but they may be willing to take that cost because their participants may be happier employees.