• Bradley C Johnston, Pablo Alonso-Coello, Jan O Friedrich, Reem A Mustafa, Kari A O Tikkinen, Ignacio Neumann, Per O Vandvik, Elie A Akl, Bruno R da Costa, Neill K Adhikari, Gemma Mas Dalmau, Elise Kosunen, Jukka Mustonen, Mark W Crawford, Lehana Thabane, and Gordon H Guyatt.
• Department of Anesthesia and Pain Medicine (Johnston, Crawford), The Hospital for Sick Children, University of Toronto, Toronto, Ont.; Institute of Health Policy, Management and Evaluation (Johnston), Dalla Lana School of Public Health, University of Toronto, Toronto, Ont.; Child Health Evaluative Sciences (Johnston), The Hospital for Sick Children Research Institute, Toronto, Ont.; Iberoamerican Cochrane Center (Alonso-Coello, Dalmau), Biomedical Research Institute Sant Pau, CIBER Epidemiologiay Salud Publica, Barcelona, Spain; Departments of Critical Care and Medicine (Friedrich), St. Michael's Hospital, Toronto, Ont.; Department of Medicine and Interdepartmental Division of Critical Care (Friedrich), University of Toronto, Toronto, Ont.; Departments of Medicine and Biomedical and Health Informatics (Mustafa), University of Missouri-Kansas City, Kansas City, Mo.; Department of Clinical Epidemiology and Biostatistics (Mustafa, Tikkinen, Neumann, Akl, Thabane, Guyatt), McMaster University, Hamilton, Ont.; Departments of Urology and Public Health (Tikkinen), Helsinki University Central Hospital and University of Helsinki, Helsinki, Finland; Department of Internal Medicine (Neumann), Pontificia Universidad Catolica de Chile, Santiago, Chile; Institute of Health and Society (Vandvik), Faculty of Medicine, University of Oslo, Oslo, Norway; Department of Medicine (Vandvik), Innlandet Hospital Trust, Division Gjövik, Norway; Clinical Epidemiology Unit (Akl), American University of Beirut, Beirut, Lebanon; Institute of Primary Health Care (da Costa), University of Bern, Bern, Switzerland; Department of Critical Care Medicine and Sunnybrook Research Institute (Adhikari), Sunnybrook Health Sciences Centre, Toronto, Ont.; Interdepartmental Division of Critical Care (Adhikari), University of Toronto, Toronto, Ont.; School of Medicine and Centre for General Practice (Kosunen), University of Tampere and Pirkanmaa Hospital District, Tampere, Finland; School of Medicine and Depar
• CMAJ. 2016 Jan 5; 188 (1): 25-32.

BackgroundMeta-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).MethodsWe 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).ResultsOverall, 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.InterpretationNone 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.© 2016 Canadian Medical Association or its licensors.

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