The whole point of the Supreme Court’s decision in Wal-Mart Stores, Inc. v. Dukes was to put an end to “trial by formula” class actions that stack the deck against defendants. Lower courts, unfortunately, haven’t gotten the message. And that is a serious threat to defendants’ due process rights, as Cato’s amicus brief in Tyson Foods, Inc. v. Bouaphakeo shows. The plaintiff class in this farcical case consists of about 1,300 workers at an Iowa pork-processing plant who say that Tyson failed to compensate them for the overtime that they spent “donning” and “duffing” protective gear. The plant has some 420 job classifications, each of which has different protective requirements, not to mention that Tyson provides additional optional gear—so even workers at the same position may wind up wearing different equipment. Logically, then, one would expect the plaintiffs to present evidence of the amount of time each person spent putting on and taking off gear, compare that to the work and pay records kept by Tyson, and then show that they weren’t properly compensated for any time they worked more than 40 hours in a given week (which triggers overtime under the Fair Labor Standards Act). But that’s not what happened. Rather than provide evidence of individual employees’ changing times, the class extrapolated from just a few examples. According to the plaintiffs’ expert, changing times ranged from a few seconds to ten minutes per employee—reflecting what even the expert acknowledged was “a lot of variation.” Regardless, the expert averaged everything out and arrived at 18 minutes for “processing” workers and 21.25 minutes for “slaughter” workers. A second expert then added those averages to individual employees’ time records, identified weeks in which workers were due overtime, and calculated damages, arriving at a class-wide figure of over $6 million in unpaid overtime wages. But, as the second expert conceded, that figure was quite sensitive to changes in the averages; reduce them by even a small amount and hundreds of workers would drop out of the class altogether. Indeed, the jury ultimately found for the employees but rejected the average times and accordingly reduced the award to about $3 million. This is incoherent. Based on the evidence, the jury necessarily believes that a substantial number of class members suffered no injury at all. Yet as class members, they’ll still receive damages—at the expense of other workers who might actually have been underpaid. Tyson, meanwhile, was denied any ability to challenge the injuries and damages of individual class members, only the plaintiffs’ formula. That’s not how litigation is supposed to work. Federal Rule of Civil Procedure 23, which sets the procedure for class actions, isn’t supposed to alter anybody’s substantive rights. That means that a class action can’t be used as a shortcut by “extrapolating” liability and damages. Proper class actions, the Supreme Court explained in Dukes, require that plaintiffs’ claims turn on a common contention—for example, whether a product was defectively designed. When that requirement is loosened, the result is “trial by formula,” which not only violates Rule 23 but also raises serious due-process concerns. When aggregate litigation procedures abridge a defendant’s ability to mount the same defenses that it could bring in individual suits, something is seriously wrong. When the Court hears this case this fall, it needs to make clear that trial by formula is off-limits.