Law profs Stephen Burbank and Sean Farhang have written Class Certification in the U.S. Courts of Appeals: A Longitudinal Study. Here is the abstract:
There is a vast literature on the modern class action, but little of it is informed by systematic empirical data. Mindful both that there have been few Supreme Court class certification decisions and that they may not provide an accurate picture of class action jurisprudence, let alone class action activity, over time, we created a comprehensive data set of class certification decisions in the United States Courts of Appeals consisting of all precedential panel decisions addressing whether a class should be certified from 1966 through 2017, and of nonprecedential panel decisions from 2002 through 2017.
In Section I, through a literature review, we identify both prior empirical scholarship and commonly asserted claims concerning federal class action activity and jurisprudence over time. In Section II we present our data and explore the light they shed on questions that have been raised, and assertions that have been made, about class action certification decisions in the U.S. Courts of Appeals. Our findings show that, contrary to conventional expectations, in the period since Wal-Mart and Comcast, plaintiffs have been winning certification appeals more frequently than they were formerly, and Rule 23(f) contributed to this recent success. This growth in pro-certification outcomes occurred on both Democratic- and Republican-Majority panels.