With stocks slumping, what should small investors do? Not to be glib, but how about nothing?

Assuming you’re satisfied with your basic, long-term investing strategy, trying to second-guess the market may do more harm than good, opening you to the perennial small-investor hazard of buying high, selling low.

Indeed, there’s peace of mind to be gained from the hands-off, stay-the-course approach — and relying on that old standby, dollar cost averaging.

Obviously, stocks face a lot of headwinds — rising interest rates and inflation, problems in Iraq, the potential for terrorist acts, election-year jitters, the impact of soaring oil prices. …

At the same time, the economy is strengthening and corporate profits are improving. There’s no telling whether the positive or negative influences will prevail during the rest of the year.

But there’s good reason to think the positive ones will prevail during the next decade.

In his best seller, “Stocks for the Long Run,” Jeremy Siegel, finance professor at the University of Pennsylvania’s Wharton School, compared the performance of stocks, long-term bonds and short-term bonds over various holding periods.

During short-term periods, stocks are unquestionably riskier. From 1802 through 2001, the biggest one-year loss suffered by the overall stock market was 38.6 percent, versus 21.9 percent for long-term bonds and 15.6 percent for short-term bonds.

But stocks also could be bigger short-term winners, with the largest one-year gain of 66.6 percent, nearly double that of long-term bonds and triple that of short-term bonds.

The performance margins narrowed as the holding periods got longer. With a 10-year holding period, something really interesting happened: Stocks became less risky than bonds.

During decade-long periods, the biggest average annual loss for stocks was 4.1 percent, versus more than 5 percent for the two types of bonds.

Stocks were still more profitable, with the largest annual gains averaging 16.9 percent, beating long- and short- bonds by about 5 points a year.

When the holding period was stretched to 20 years or more, stocks, on average, were profitable even in their worst years. Bonds, in their worst years, were losers.

Siegel also looked at how often stocks beat the two types of bonds over various holding periods from 1871 through 2001.

During one-year periods, stocks beat long-term bonds 60.3 percent of the time, and short-term bonds 64.1 percent of the time.

The longer the period, the better for stocks. With a 10-year period, stocks beat the two types of bonds more than 80 percent of the time. During 30-year periods, stocks always beat bonds.

Siegel also found that over long periods stocks were the only investment that consistently provided enough profit to significantly overcome erosion from inflation.

From 1926 through 2001, stocks returned 6.9 percent a year, after adjusting for inflation. Long-term bonds returned just 2.2 percent, short-term bonds 0.7 percent.

There’s no guarantee the patterns Siegel found will prevail in the future. But it’s risky to assume some new pattern will emerge — and especially risky to assume you can figure out what it will be.

So it’s best to rely on the truisms, which gets us back to dollar cost averaging.

Basically, this means investing the same amount of money at regular intervals, such as every month or quarter. If you have a 401(k), you’re doing this. You could do it with an ordinary taxable account by giving your broker or fund company authority to automatically draw money from your checking account at regular intervals.

The biggest benefit is discipline. Instead of sitting on a pile of cash trying to second-guess the market, you put your money to work.

And there’s a mathematical bonus. A hundred dollars invested when stock prices are down buys more shares than the same amount invested when stock prices are up. Over time, this allows you to minimize the average price you pay per share.

The lower the average purchase price, the higher the profit when you sell (or lower the loss).

That’s a pleasing thought when the market isn’t doing very well.