NEW YORK — The day-to-day price swings in the stock market this summer have gotten bigger, prompting fresh bouts of squeamishness in investors who shudder at the mere mention of a 100-point plunge.

After a 235-point surge Monday and Tuesday, the Dow Jones industrial average followed up in the past two sessions with a tiny 3-point loss to 11,100 (thanks largely to giving back all of an 85-point intraday gain yesterday).

The market's fade yesterday signals that the get-me-out-of stocks mentality that permeated Wall Street after the Dow fell 288 points on July 12 and 13, on the heels of a 135-point decline on July 7, has yet to be fully exorcised from investors' fragile psyches.

The return of risk, the dirty four-letter word Wall Street abhors, is testing investors' ability to stomach the growing volatility. It's prompting some of them to reduce the amount of risk in their portfolios.

Who can blame them? Risk is everywhere. There's interest-rate risk. Geopolitical risk, including conflict in the Middle East. Headline risk. Not to mention worries about inflation and $3 gas.

The headline on a recent research report from Societe Generale economist Stephen Gallagher sums up the angst: "Risk Aversion II — The Summer 2006 Hit."

The fear of losing money is affecting investors' decisions. Many have sold stocks and sought the safety of cash.

One Wall Street guru says the angst may be misplaced. If you cut through the "noise," bad news and daily market gyrations, Richard Bernstein, chief investment strategist at Merrill Lynch, says he reminds investors of a simple risk-reduction tool: "time."

"The probability of losing money in an investment generally decreases as the investment horizon lengthens," Bernstein says.

There's a 46 percent chance of losing money when investing in the Standard & Poor's 500 index for one day, data from Merrill Lynch Investment Strategy dating back to 1985 show.

But the odds of losses decrease as time goes on. The chances of losing money in the S&P 500 with a one-year holding period drop to 18 percent. And they decrease to zero with a 10-year holding period.

Investors, therefore, should ignore the "noise" associated with daily market moves, Bernstein says.

Reducing risk by lengthening holding periods is not a new concept. Still, if you have time to ride out the market's rough patches and have built a diversified portfolio that allows you to sleep at night (as opposed to having 100 percent riding on one stock or sector), staying the course will likely prove rewarding.

A study by Ibbotson Associates showed that an investor with a portfolio that included a mix of large-cap stocks and U.S. government bonds never had a negative return in any rolling 10-year period dating to 1926.

Still, skeptics say studies showing the virtues of a buy-and-hold strategy are flawed. Tony Ogorek, founder of Ogorek Wealth Management, dubs them "misleading."

"As a theoretical proposition, it is true. But when you attach humans to it, its track record is far worse ... because it ignores the reality of human nature," Ogorek says. "Ninety-eight percent of investors do not have the staying power during those gut-wrenching periods to stay the course."

The recent spike in volatility on Wall Street will make it even more difficult for investors to hold on, adds Harvey Hirschhorn, portfolio strategist at Bank of America.