Risk difference estimation and reporting in systematic reviews

2012 Auckland

Alonso-Coello P¹, Carrasco-Labra A², Brignardello-Petersen R³, Neumann I⁴, Akl E⁵, Sun X⁶, Johnston B⁷, Busse J⁸, Dahm P⁹, Glujovsky D¹⁰, Iorio A⁸, Irfan A¹¹, Martinez L¹, Ramirez-Morera A¹², Solá I¹, Sultan S¹³, Tikkinen K¹⁴, Vandvik P¹⁵, Zhang M⁸, Briel M¹⁶, Granados C⁸, Mustafa R⁸, Guyatt G⁸

¹Iberoamerican Cochrane Centre. Institute of Biomedical Research (IIB Sant Pau) Barcelona, Spain

²Evidence Based Dentistry Unit, Faculty of Dentistry, Universidad de Chile, Chile

³Romina Brignardello-Petersen

⁴Department of Medicine, Pontificia Universidad Catolica de Chile, Santiago, Chile

⁵Department of Medicine, State University of New York at Buffalo, NY, USA

⁶Centre for Health Research, Kaiser Permanente Northwest, Portland, Oregon

⁷Research Institute, Child Health Evaluative Sciences, The Hospital for Sick Children, Toronto, Canada

⁸Department of Clinical Epidemiology & Biostatistics, McMaster University, Canada

⁹Department of Urology, College of Medicine, University of Florida, Gainesville, Florida, USA

¹⁰Argentine Cochrane Centre IECS (Institute for Clinical Effectiveness and Health Policy), Buenos Aires, Argentina

¹¹Internal Medicine Residency Program, University of Illinois at Urbana-Champaign

¹²CCSS Permanent Medical Advisor, Health Care Development Division, IHCAI FOUNDATION & Central America Cochrane Branch-associated Fellow, Costa Rica

¹³Division of Gastroenterology, Hepatology, and Nutrition, Malcom Randall Veterans Affairs Medical Center, University of Florida College of Medicine

¹⁴Dept. of Urology, Helsinki University Central Hospital, Helsinki, Finland

¹⁵Norwegian Knowledge Centre for the Health Services, Oslo, Norway

¹⁶Basel Institute for Clinical Epidemiology and Biostatistics, University Hospital Basel, Switzerland

Background:

Intervention effects can be presented alternatively in relative (such as relative risk) or absolute terms (such as risk difference). To avoid misleading users systematic reviews (SRs) authors should include both absolute and relative estimates. There is limited information about this topic and there are important potential implications for decision-making in healthcare. We therefore believe it is important to explore how this issue is managed in published systematic reviews.

Objectives:

To determine the proportion of SRs reporting absolute effects (AE) and to evaluate how these are derived and interpreted. Additionally, we will explore the association of pre-specified study characteristics with the report of AE.

Methods:

We searched the Medline and the Cochrane Database of Systematic Reviews for systematic reviews of randomized controlled trials published in 2010 and reporting a meta-analysis of dichotomous outcome(s). After teams of two reviewers screened studies for eligibility, we randomly selected 75 Cochrane and 75 non-Cochrane reviews. Teams of two reviewers are currently abstracting data using standardized, piloted forms and written instructions.

Results:

Data abstraction is ongoing. The results of analyses will be available for presentation at the colloquium.

Conclusions:

Our results will inform the extent of limitations of determining and reporting AE in SRs and lay the foundation for further studies about the potential implications for decision-making.