The size of federal class action lawsuits accusing companies of securities fraud has dropped significantly, new studies show, as the bull market in stocks approaches its sixth birthday.

Losses claimed by shareholders, measured by how much stock prices fell when alleged frauds were disclosed, shrank 45 percent in 2014 to an eight-year low of $57 billion, a study released Tuesday by Cornerstone Research and Stanford Law School showed.

One cause may be that shareholders have been aiming at smaller targets. Only 11 companies in the Standard & Poor’s 500 were hit with class actions. That is fewer than in any year for which data has been collected since 2000, Cornerstone said.

Settlements are also getting smaller.

The average size dropped to $34 million, a three-year low, in 2014 from $86 million a year earlier, a study released last week by NERA Economic Consulting shows. Just 94 cases were resolved in 2014, matching the fewest since 1996, NERA said.

Class action lawsuits swelled in size in the wake of steep stock market losses during the global financial crisis.

Stock prices on the S&P 500 have nearly tripled from their March 2009 lows, while the Nasdaq has nearly quadrupled.

Class action lawsuits were bigger and more frequent after steep stock market losses during the global financial crisis. Stock prices on the S&P 500 have nearly tripled from their March 2009 lows, while the Nasdaq has nearly quadrupled.

“The passage of financial crisis cases, and the bull market, have impacted the number and magnitude of cases,” said Jacob Zamansky, a New York lawyer who represents plaintiffs in securities class actions. “We will see plenty of fraud and misconduct by issuers and banks, which is keeping us busy.”

Securities class actions accuse companies of making false or misleading statements, or concealing bad news they should have disclosed, causing investors to overpay for their shares.

Cornerstone said plaintiffs filed 170 such lawsuits in 2014, up from 166 a year earlier, but below the average of 188 from 1997 to 2014.

NERA said one reason there are fewer settlements may be that companies are “holding off,” hoping plaintiffs will not be able to show that alleged misrepresentations actually affected stock prices.

That was a requirement imposed in a June 2014 decision by the U.S. Supreme Court in favor of Halliburton Co, the oil services company.

The court, however, rejected calls to use that case to overturn a 1988 precedent, Basic Inc v Levinson, that underpins the modern class action industry.