NEW YORK — Think Dow 11,000 is a big deal? Think again.

The Dow Jones industrial average briefly hit the milestone Friday for the first time in 18 months before closing at 10,997.

But Wall Street analysts who study key stock index levels say all the attention paid to 11,000 is more like a big distraction. They worry that investors are ignoring another number at their peril: The surprisingly low volume of trading. As stocks have risen over the past year, the volume reflects the vulnerability of a rally riding on the shoulders of relatively few participants.

And that has given pause even to the bulls.

“It worries a lot of us,” says Wellington Shields’ Frank Gretz, a technical analyst who specializes in pinpointing market levels at which stocks might suddenly rise or fall. He wonders whether the volume signals that the rally could soon peter out, like the big surges that preceded steep declines in the 1930s in the U.S. and in Japan more recently.

Louise Yamada, a 29-year veteran of technical analysis who heads an eponymous firm in New York, says she’s not just concerned but confused.

“Why is the market going up?” she asks. “You usually don’t see advances without volume.”

The widely cited Dow index, which tracks stocks of 30 companies, is up 70 percent from its lows of more than a year ago. The climb has been one of the strongest in history, and it may herald a strong recovery. But it has been propelled by relatively few trades.

The 200-day moving average volume on the New York Stock Exchange is now at 1.2 billion shares, down from 1.6 billion, or nearly 25 percent, a year ago.

In other words, if there is wisdom in crowds, the stock market is getting dumber.

One reason volume is lower: Main Street investors have largely stayed out of the market, abandoning it to hedge funds, pension funds and other professional investors. Last year, individuals, as tracked by mutual fund flows, yanked $14 billion from stock mutual funds.

Bulls argue that the Dow breaching 11,000 might convince ordinary investors that the rally will last. And that will bring a flood of money into the market, pushing indexes higher.

But Janney Montgomery Scott analyst Dan Wantrobski isn’t convinced.

“Main Street investors need confidence in the economy more than the Dow at 11,000,” he says. “They need a drop in the unemployment rate.”