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ISM nonmanufacturing data, reported at 10 a.m. ET, is expected to show continued expansion at 53.5, up from 53. The sharp drop in ISM manufacturing data, however, has traders cautious about the services sector number. The drop in manufacturing activity triggered a decline of over 300 points in the Dow, on concerns the U.S. economy is slowing at the same time the Fed is moving away from its easy money policy.
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On Tuesday, stocks recovered some ground after Monday's big selloff, with the Dow up 72 at 15,445, and the S&P 500 up 13 at 1,755. The Nasdaq was the biggest gainer, up 34 at 4,031.
"There's still some downside ... still lots of momentum," said Clifford Noreen, president of Babson Capital, adding that he does not expect a much bigger correction. The S&P 500 has lost about 5 percent so far.
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There are signs that the selloff will not be deep, Noreen said, and one of those is coming from the credit market. The high-yield bond market is a leading indicator for equity market selloffs, he added, but it has held in and spreads have only widened about 5 basis points.
"It tells you the equity market is not going down that much further," he said.
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Noreen does not expect the emerging markets to become a big issue for stocks, nor does he foresee the selloff in Japan to affect U.S. equities. The Nikkei is down 14 percent since the beginning of the year.
"It's the market that went up the most," he said.
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Besides data, traders are watching another batch of earnings Wednesday.
Merck, Time Warner, Humana, Automatic Data, GlaxoSmithKline, Allergan, Estée Lauder, and W.R. Grace report before the open.
Twitter reports its first earnings as a public company after the bell. Yelp, Allstate, Green Mountain, Disney, Pandora, Solera, Standard Pacific, Tesoro, Fiserv, Akamai and Shutterfly also report after the closing bell.
—By CNBC's Patti Domm; follow her on Twitter @pattidomm.