Subgroup analyses in systematic reviews: a survey of Cochrane and non-Cochrane reviews

2012 Auckland

Sun X¹, Brignardello-Petersen R², Carrasco-Labra A², Neumann I³, Alonso-Coello P⁴, Akl E⁵, Johnston B⁶, Briel M⁷, Busse J⁸, Dahm P⁹, Granados C⁴, Glujovsky D¹⁰, Iorio A⁸, Irfan A¹¹, Martinez L⁴, Reem Mustafa RM⁸, Ramirez-Morera A¹², Sola I⁴, Sultan S¹³, Tikkinen K¹⁴, Vandvik P¹⁵, Zhang M⁴, Guyatt G⁴

¹Centre for Health Research, Kaiser Permanente Northwest, Portland, Oregon, USA

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

³Department of Medicine, Pontificia Universidad Catolica de Chile, Santiago, Chile

⁴Iberoamerican Cochrane Centre, Institute of Biomedical Research (IIB Sant Pau), Barcelona, Spain

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

⁶Research Institute, Child Health Evaluative Sciences, The Hospital for Sick Children, Toronto, Canada

⁷Basel Institute for Clinical Epidemiology and Biostatistics, University Hospital Basel, Switzerland

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

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

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

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

¹²CCSS, 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

Background:

Studies included in a meta-analysis often differ in methodological, patient, and intervention characteristics, and outcome measures, differences that may result in heterogeneity of treatment effects. Subgroup analyses may explain such heterogeneity. However, both inappropriate conduct and reporting of subgroup analyses may lead to misguided clinical and policy decisions, and the extent to which systematic review authors undertake subgroup analyses and the quality of their conduct and reporting remain uncertain.

Objective:

To examine the extent to which subgroup analyses are conducted, and to compare the quality of conduct and reporting of subgroup analyses between Cochrane versus non-Cochrane reviews.

Methods:

We searched the Cochrane Database of Systematic Reviews and the Medline for systematic reviews published in 2010 that included a meta-analysis of dichotomous outcome reported in randomized controlled trials. Teams of two reviewers screened studies for eligibility. We randomly selected 75 Cochrane and 75 non-Cochrane reviews from eligible studies. Teams of two reviewers are currently abstracting data using standardized, piloted forms guided with written instructions We will focus on subgroup analyses of aggregate data meta-analyses, and the unit of analysis is an individual systematic review. Our analysis will examine whether authors planned to explore heterogeneity, whether they were able to explore heterogeneity, reasons for the failure of exploring heterogeneity, and approaches to exploring heterogeneity. We will examine whether a subgroup hypothesis was pre-specified, the number of subgroup hypotheses tested, the number of outcomes and corresponding effect measures used for subgroup analyses, and whether a test of interaction was used. For each major issue, we will compare practice in Cochrane versus non-Cochrane reviews.

Results:

The results of analyses will be available for presentation at the colloquium.

Discussion:

The results of this study will provide an important insight about the quality of conduct and reporting of subgroup analyses in systematic reviews.