The likelihood of plaintiffs opting out of class action settlements and continuing to pursue their own litigation may be increasing, which could result in more court system inefficiencies, says a study issued Thursday.

San Francisco-based Cornerstone Research said 8.9% of plaintiffs opted out of settlements between 2014 and 2018, compared with an opt-out rate of 3.4% before 2004, according to the report, Opt-Out Cases in Securities Class Action Settlements.

There is a correlation between the size of the class action settlements and the rate of opt-outs, according to the report. The report said while cases with settlements of more than $20 million account for only 26% of the 2014-2018 settlements, they represent more than 80% of the opt-out cases that were identified over that period.

There was a similar effect among the largest “mega” settlements, with 15 of 23 cases with settlements of more than $500 million in 1996-2018 having associated cop-outs, according to the report.

And all four cases with settlements of more than $500 million in 2014-2018 had associated opt-outs, compared with 7.4% of class action settlements below $500 million, the report said.

“Across all class action settlements between 1996 and 2018, 65% with settlements of at least $500 million had a least one related opt-out, compared with less than 4% of settlements below $500 million,” said the report.

“If opt-outs become filed more frequently, it may result in inefficiencies for all parties in the court system, as courts may struggle with a higher caseload, defendants may spend more on legal fees, and plaintiffs may face more uncertainty about the n necessity of opting out or remaining in classes,” the report said.

The report found also a change in the most common plaintiffs in opt-out cases. Pension funds accounted for almost half of the pre-2014 opt-outs, according to the report, while non-pension institutional investors, including mutual funds, hedge funds and other investment management firms, were parties in 15 of the 34 opt-outs in 2014-2018, the report said.

Cornerstone issued a report earlier this month that said shareholders litigated 82% of merger & acquisition deals valued over $100 million in both 2017 and 2018.