By Steven M. Klepper

The Supreme Court of Maryland adopted the federal Daubert standard for admission of expert testimony in 2020.1 Given that Daubert rulings are discretionary, the abuse-of-discretion standard governs appellate review of expert testimony.2 During the summer of 2023, the Supreme Court of Maryland issued three opinions holding that trial judges abused their discretion—at least in part—when they admitted or excluded expert testimony.3 In the last of the three cases, Justice Brynja Booth authored a concurring opinion noting how the Court was applying less deference than in other discretionary contexts, and she urged her colleagues to clarify the nature of review.4 This article posits that Daubert errors fall into two main categories: procedural and substantive. Procedural errors occur when a trial court misunderstands an aspect of the Daubert framework.5 In effect, the trial judge has misread Maryland Rule 5-702, which governs expert testimony. 6 A misreading of an evidentiary rule is a legal error that is reviewed de novo, meaning without deference. 7 Substantive error occurs when a trial judge follows the Daubert framework but reaches a result to which an appellate courts cannot defer because either the trial judge has abused their8 discretion in the traditionalsense or the Supreme Court of Maryland has decided to draw a boundary circumscribing all trial judges’ discretion.9 Such vocabulary not only accurately describes the nature of judicial review but also reduces friction between trial judges and appellate courts