RT Journal Article SR Electronic T1 Do clinicians understand the size of treatment effects? A randomized survey across 8 countries JF Canadian Medical Association Journal JO CMAJ FD Canadian Medical Association SP 25 OP 32 DO 10.1503/cmaj.150430 VO 188 IS 1 A1 Bradley C. Johnston A1 Pablo Alonso-Coello A1 Jan O. Friedrich A1 Reem A. Mustafa A1 Kari A.O. Tikkinen A1 Ignacio Neumann A1 Per O. Vandvik A1 Elie A. Akl A1 Bruno R. da Costa A1 Neill K. Adhikari A1 Gemma Mas Dalmau A1 Elise Kosunen A1 Jukka Mustonen A1 Mark W. Crawford A1 Lehana Thabane A1 Gordon H. Guyatt YR 2016 UL http://www.cmaj.ca/content/188/1/25.abstract AB Background: Meta-analyses of continuous outcomes typically provide enough information for decision-makers to evaluate the extent to which chance can explain apparent differences between interventions. The interpretation of the magnitude of these differences — from trivial to large — can, however, be challenging. We investigated clinicians’ understanding and perceptions of usefulness of 6 statistical formats for presenting continuous outcomes from meta-analyses (standardized mean difference, minimal important difference units, mean difference in natural units, ratio of means, relative risk and risk difference).Methods: We invited 610 staff and trainees in internal medicine and family medicine programs in 8 countries to participate. Paper-based, self-administered questionnaires presented summary estimates of hypothetical interventions versus placebo for chronic pain. The estimates showed either a small or a large effect for each of the 6 statistical formats for presenting continuous outcomes. Questions addressed participants’ understanding of the magnitude of treatment effects and their perception of the usefulness of the presentation format. We randomly assigned participants 1 of 4 versions of the questionnaire, each with a different effect size (large or small) and presentation order for the 6 formats (1 to 6, or 6 to 1).Results: Overall, 531 (87.0%) of the clinicians responded. Respondents best understood risk difference, followed by relative risk and ratio of means. Similarly, they perceived the dichotomous presentation of continuous outcomes (relative risk and risk difference) to be most useful. Presenting results as a standardized mean difference, the longest standing and most widely used approach, was poorly understood and perceived as least useful.Interpretation: None of the presentation formats were well understood or perceived as extremely useful. Clinicians best understood the dichotomous presentations of continuous outcomes and perceived them to be the most useful. Further initiatives to help clinicians better grasp the magnitude of the treatment effect are needed.