Subprime mortgage and auction-rate securities cases contributed to a sharp increase in the number of shareholder class action filings in the first half of 2008, according to a study issued yesterday.

Driven in part by the meltdown of the subprime mortgage and credit markets, the number of filings is projected to reach almost 280 by the end of the year, the largest annual total since 2002 and more than double a low of 131 in 2006, a report from NERA Economic Consulting, an economics analysis firm, said. Of the filings through June, 51% are related to the subprime crisis.

Despite the uptick in the number of filings since 2006, the average settlement values have remained steady, at around $30 million, the study found. But excluding settlements of more than $1 billion, lawsuits settled this year for $10 million on average, a noticeable decline from settlements in recent years, when the average has hovered between $20 million and $30 million.

The decrease could be attributed to decisions by the Supreme Court to limit the damages awarded in class action suits. “Only 2% of all settlements during these six months were $100 million or more, as opposed to 7% in 2007 and almost 10% in 2006,” an author of the study, Svetlana Starykh, said. The study comes on the heels of another report by Stanford University’s Securities Class Action Clearinghouse, which found that the number of filings rose to 110 in the first six months of this year, up from a low of 53 in the second half of 2006.