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of all precedential panel decisions addressing whether a class should be certified from 1966 through 2017, and of nonprecedential panel decisions from 2002 through 2017.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.
We find that final-judgment appeals, at least in precedential decisions, played a larger role in this landscape prior to Rule 23(f) than has often been asserted or assumed, and that in all decisions since 2002 they continue to play a major role. We also find that final-judgment appeals involving (b)(3) issues are common among appeals, which casts doubt on the conventional wisdom concerning the class certification decision as the “death knell” for plaintiffs or defendants in such cases.
We find significant variation over time in appeal outcomes under Rule 23(f), with defendants far more successful than plaintiffs prior to Wal-Mart and Comcast, and relative parity after. This variation suggests the hazards of generalizing about operation of that rule from experience in any particular period. Our models also show that, for reasons about which we can only speculate, interlocutory appeals since around 2000 have elicited more ideological voting behavior by judges, leading to greater polarization.