The number of class-action plaintiffs opting out of settlements to pursue their own litigation has risen in recent years, according to a report issued Wednesday by Cornerstone Research.

While the optout rate was 3.2% in 2014, the number has grown, averaging 8.9% between 2015 and 2018, when the optout rate was 13.2%.

Pension funds, which previously appeared in almost half of the pre-2014 class-action cases, appeared in just four class-action cases between 2014 and 2018 in which parties were able to be identified, according to the report, titled “Opt-Out Cases in Securities Class Action Settlements.” Non-pension institutional investors such as sovereign wealth funds and hedge funds were parties in 15 of the 34 class actions between 2014 and 2018, out of a total 382 securities class-action settlements.

A key factor in the recent trend might be the 2017 Supreme Court decision in California Public Employees’ Retirement System vs. ANZ Securities Inc., limiting the time investors have to decide whether to join securities class-action lawsuits. That might have persuaded more plaintiffs to opt out pre-emptively so they could preserve their right to sue, the report’s authors said.

Rather than discouraging investors from opting out, recent court rulings including the CalPERS decision “may instead result in more and earlier optouts by plaintiffs with deeper pockets, such as institutional investors,” the report said.

Another factor in the increase in optouts is the size of the settlements, said co-author Christopher Harris, who co-chairs the complex litigation group at Latham & Watkins. “We are continuing to see that the size of the settlements impacts the decision. It is only worth the money to opt out in a large case,” Mr. Harris said in an interview.