Shares of Fair Isaac Corp. dropped more than 20% Monday after an analyst said the developer of credit-scoring systems could report weak scoring volume figures.

Michael B. Nemeroff, a Wedbush Morgan Securities analyst, lowered his stock rating for the maker of the widely used FICO credit score to "sell," from "hold," saying investors could be disappointed by results for its fiscal second quarter, which ended March 31.

Fair Isaac is expected to release its financial results Wednesday.

The shares have risen almost 80% in a little over a month. "The recent share price run-up could suggest investors are expecting an upturn to the company's scoring business this quarter by incorrectly using the recent surge in mortgage refinancings as a proxy for an improving consumer credit environment," Nemeroff wrote in a note to clients.

However, rising unemployment rates and record chargeoffs in credit cards are likely a better indicator of how U.S. consumers are faring, he wrote.

A representative from Fair Isaac could not be reached for comment Monday.

By Monday afternoon, the shares were down 20.45% from Friday's closing price, to $14.51. The company's shares were trading as high as $27.84 in September, but last month they fell to $9.76, the lowest intraday point since 1999.

Nemeroff wrote that investors could be disappointed with Fair Isaac's earnings, and that the shares could fall if investors are expecting a sharp turnaround in scoring revenue.

The fiscal second-quarter revenue will be in line with or slightly below his estimates, as a result of continued low scoring volume and financial institutions' unwillingness to spend, he wrote.

In addition, Nemeroff wrote that there is a lag of about one quarter between any pickup in Fair Isaac's transaction volume and when the company books the revenue.

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