LAUSR

Wampold et al. (1997) reported a landmark metaanalysis concluding that “the efficacy of bona fide treatments are roughly equivalent” [p.203]. Crucially, the authors applied three stringent criteria to the selection of studies: direct comparisons between treatments, named treatments rather than general types, and bona fide treatments as opposed to alternate treatments. They showed all effects to centre around zero and yield a maximum true effect size (ES d) difference of .21, providing support for the Dodo Bird verdict of no real – or at best, small – differences between the effectiveness of bona fide psychological therapies. Twenty-five years on, the article has achieved high impact – in the region of 1700 Google Scholar citations and 700 Web of Science (WoS) citations, twice that of the next highest-cited relevant article in WoS – and can reasonably be viewed as the high watermark of the Dodo Bird argument. Clinically, the article has done much to protect the collective body of bona fide psychological therapies, providing practitioners and patients with treatment options within the context of an ever-increasing and diverse population in need of psychological help. For research, it marked a turning point in the argument of there being a dominant single therapy modality and enabled the focus to move away from considering only differences between therapies and move towards investigating areas of variability both between and within therapies. Of course, there are subtle differences between treatment modalities, often masked by meta-analyses (e.g., by classification categories of treatments) and by group mean comparisons taken at a single time point (e.g., Baldwin & Imel, 2020). While it might be argued that single studies do not outweigh metaanalytic findings, they may act as more sensitive indicators of differences derived from “same experiment data”. For example, a recent large (N >500) pragmatic, non-inferiority randomized trial comparing cognitive behavioural therapy (CBT) with personcentred experiential therapy (PCET), embedded in routine practice and satisfying Wampold et al.’s three inclusion criteria, found no significant difference between treatments at 6-months but at 12 months favoured CBT (ES = 0.27; Barkham et al., 2021). Effects are not static; they can change over time post-therapy and also across the course of therapy, as evidenced in a large practice-based study where patient gains in initial sessions significantly and differentially favoured non-directive supportive therapy but in later sessions favoured CBT (Pybis et al., 2017). Such subtle differences between therapies might have important implications for treatment assignment but are lost when considering results at an overall group level. The counterpoint is that smaller differences are not important. But consider the maths. A traditional ES (d) of .20 is equivalent to an 11% difference in outcomes between therapy conditions (i.e., affecting 110 people per 1000 treated). In the English Improving Access to Psychological Therapies (IAPT) programme, hundreds of individual services treat thousands of patients each year and the national