Sep. 9--After the collapse of Lehman Brothers a year ago led to a sickening slide in the stock market, many individual investors yanked their money out of stocks.

But a year later, research shows that most investors stuck with their investing plans -- because they had faith in the long-term prospects of the stock market, or simply because it was easier to do nothing.

Depending on which data you look at, only 3 percent to 5 percent of assets came out of stock market mutual funds held by individual investors and retirement savers.

"It absolutely surprised us," said Pam Hess, director of retirement research at Hewitt Associates, the large Illinois-based employee benefits consulting firm. "We remain surprised that so many people stayed the course. We thought it could have been much more dramatic. We had many people say, 'I just don't know what to do.' "

As it happens, doing nothing is often the right choice, advisers say. It's rarely a good idea to make radical investment changes in response to market shocks. Investors, experts say, should choose a mix of stocks, bonds and cash that makes sense for their age, risk tolerance, and time horizon, and then basically stick with it, whether the Dow zooms or swoons.

Generally, young people with a long time horizon should focus on stocks, which are volatile, but offer higher long-term returns. Older workers with only a few years till retirement are typically advised to tilt more toward bonds.

But being too conservative can backfire. A new study from Financial Engines, a California financial advisory firm, says that retirement savers who abandoned stocks in favor of more conservative portfolios last year will have to continue working a year or more longer than people who stuck with a mix of stocks and bonds.

"The low expected growth of these conservative portfolios, which may protect from short-term losses, can do more harm to near-retirees' retirement outlooks than was done by the large 2008 losses," Financial Engines concluded.

In the year since the financial markets' meltdown, investors gradually have grown more hopeful about both the stock and bond markets. From September 2008 to March 2009, investors pulled out more money than they put into stock mutual funds almost every month, according to the Investment Company Institute, the trade association for the mutual fund industry.

But investor psychology seemed to shift in April, as the Dow Jones average began trending upward from a low around 6,500 in early March and the economy showed signs of stabilizing.