THE stock market has changed considerably since early 2000, when the Standard & Poor’s 500-stock index traded at a record high valuation.

Today, stocks are only about half as expensive, based on their price-to-earnings ratios. And they’ve become a bit cheaper lately: the S.& P. 500 has fallen by more than 7 percent since Jan. 19. Yet in at least one important respect, there may be a significant parallel to the situation at the height of the tech bubble. Many market watchers say the late-January sell-off this year could be a sign that the market is again “priced for perfection,” said David C. Wright, managing director of Sierra Investment Management in Santa Monica, Calif.

“Investors have already priced in everything we can hope for in terms of an economic and profit recovery,” he said. Stocks rallied 65 percent from March 9 to Dec. 31 last year, and it may be unrealistic to expect that kind of advance now.

“Investors are expecting another Goldilocks scenario,” he said, adding that economically disappointing news is now likely to drive the markets lower in the coming months.