Challenging a "Gold Standard" in Rehabilitation Research: The Limits of Outcome-Centered Trials in Pain Science

Randomized controlled trials (RCTs) hold a privileged position in evidence hierarchies and are widely regarded as the most rigorous design for evaluating rehabilitation intervention efficacy. However, their conventional structure, which focuses on group-level average treatment effects assessed at sparse time points and abstains from a deeper inquiry into individual differences (ie, outcome-centered), presents critical limitations when applied to complex phenomena such as chronic pain. These limitations are often under recognized, reinforcing a narrow view of causality that discourages methodological pluralism and constrains the advancement of rehabilitation-oriented pain science. To address this gap, this article examines what outcome-centered trial designs can and cannot tell us in pain research, and how other approaches can contribute. The article discusses the historical and theoretical foundations of the model's widespread adoption, then examines its practical and inferential shortcomings through common design and analytical choices, and finally explores how alternative designs and modeling strategies offer distinct contributions in clarifying the sources and patterns of variation in intervention effects. Rather than treating RCTs as inherently superior, this article advocates judging them by how well methods match the research question and phenomenon studied. Advancing more precise, theory-informed, and clinically relevant evidence requires recognizing both the capacities and limitations of each methodological approach, including large-sample outcome-centered RCTs, and moving beyond rigid hierarchies that rank designs independently of context.