A new congressional study adds statistical support to what most shareholders already know: Inaccurate corporate financial statements have cost investors billions of dollars in recent years.

The General Accounting Office report released yesterday is the first government attempt to measure the effect of accounting scandals at Enron Corp. and several other companies over the past few years.

The study found that 10 percent of publicly traded companies restated financial statements because of accounting irregularities from January 1997 to June 2002. It said these corrections cost investors, on average, 10 percent of their stock's value from the day before to the day after restatements and 18 percent of their stock's value from 60 days before to 60 days after corrections.

The study also found that the number of companies restating financials each year increased 145 percent during the same period. The report said that based on restatements so far this year, it expects the trend to continue. AOL Time Warner Inc., for instance, issued a restatement yesterday.

"We estimate that the restating companies lost about $100 billion in market capitalization" in the days after restatements, the report said. That is "significant for the companies and shareholders involved," it said, even though it represents less than half of 1 percent of the market capitalization of the country's major stock exchanges.

"In a number of the restating companies we identified, corporate management, boards of directors, and auditors failed in their roles, as have securities analysts and credit rating agencies that did not identify problems before investors and creditors lost billions of dollars," the study said.

Senate Banking Committee Chairman Paul S. Sarbanes (D-Md.), who requested the study, said in a prepared statement that the results "demonstrate that investors have suffered significant financial harm" because of restatements.