Oakmark funds are known for fairly concentrated portfolios.

That conclusion may have encouraged some to favor concentrated portfolios, he said.

That highly concentrated portfolio means declines in just a few stocks could send the fund reeling.

"These are unique - diversified funds with concentrated portfolios."

Such funds also wind up with less concentrated portfolios.

Until recently, he held most of his family's liquid assets in a concentrated portfolio of four or five stocks.

Combine the two and - bingo - you start another trend, funds in which two or more star managers run a concentrated portfolio.

In other words, it may take just a mistake or two in a concentrated portfolio to wreck an investor's year.

Oakmark Select, with $514 million in assets, is a concentrated portfolio of midsize and large stocks.

Because of its relatively concentrated portfolio, the fund is oftenmore volatile than diversified funds.