title: Systematic reviews experience major limitations in reporting absolute effects.
abstract: OBJECTIVE
  Expressing treatment effects in relative terms yields larger numbers than expressions in absolute terms, affecting the judgment of the clinicians and patients regarding the treatment options. It is uncertain how authors of systematic reviews (SRs) absolute effect estimates are reported in. We therefore undertook a systematic survey to identify and describe the reporting and methods for calculating absolute effect estimates in SRs.
  
  
  METHODS
  Two reviewers independently screened title, abstract, and full text and extracted data from a sample of Cochrane and non-Cochrane SRs. We used regression analyses to examine the association between study characteristics and the reporting of absolute estimates for the most patient-important outcome.
  
  
  RESULTS
  We included 202 SRs (98 Cochrane and 104 non-Cochrane), most of which (92.1%) included standard meta-analyses including relative estimates of effect. Of the 202 SRs, 73 (36.1%) reported absolute effect estimates for the most patient-important outcome. SRs with statistically significant effects were more likely to report absolute estimates (odds ratio, 2.26; 95% confidence interval: 1.08, 4.74). The most commonly reported absolute estimates were: for each intervention, risk of adverse outcomes expressed as a percentage (41.1%); number needed to treat (26.0%); and risk for each intervention expressed as natural units or natural frequencies (24.7%). In 12.3% of the SRs that reported absolute effect estimates for both benefit and harm outcomes, harm outcomes were reported exclusively as absolute estimates. Exclusively reporting of beneficial outcomes as absolute estimates occurred in 6.8% of the SRs.
  
  
  CONCLUSIONS
  Most SRs do not report absolute effects. Those that do often report them inadequately, thus requiring users of SRs to generate their own estimates of absolute effects. For any apparently effective or harmful intervention, SR authors should report both absolute and relative estimates to optimize the interpretation of their findings.
authors.affiliation: Clinical Epidemiology and Public Health Department, Iberoamerican Cochrane Centre, Biomedical Research Institute Sant Pau (IIB Sant Pau), C/ Sant Antoni Maria Claret, 167, Pavelló 18, planta 0, 08025 Barcelona, Spain; Centro de Investigación Biomédica en Red de Epidemiología y Salud Pública (CIBERESP); Department of Clinical Epidemiology & Biostatistics, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada. Electronic address: PAlonso@santpau.cat.
authors.forename: Pablo
authors.initials: P
authors.lastname: Alonso-Coello
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada; Evidence-Based Dentistry Unit, Faculty of Dentistry, Universidad de Chile, Sergio Livingstone 943, Santiago, Chile.
authors.forename: Alonso
authors.initials: A
authors.lastname: Carrasco-Labra
authors.affiliation: Evidence-Based Dentistry Unit, Faculty of Dentistry, Universidad de Chile, Sergio Livingstone 943, Santiago, Chile; Institute of Health Policy, Management & Evaluation, University of Toronto, 4th Floor, 155 College St, Toronto, Ontario M5T 3M6, Canada.
authors.forename: Romina
authors.initials: R
authors.lastname: Brignardello-Petersen
authors.affiliation: Department of Medicine, Pontificia Universidad Católica de Chile, Avenida Libertador Bernardo O Higgins 340, Santiago, Región Metropolitana, Chile.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Neumann
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada; Department of Internal Medicine, American University of Beirut Medical Center, P.O. Box: 11-0236, Riad-El-Solh, Beirut 1107 2020.
authors.forename: Elie A
authors.initials: EA
authors.lastname: Akl
authors.affiliation: Clinical Epidemiology and Public Health Department, Iberoamerican Cochrane Centre, Biomedical Research Institute Sant Pau (IIB Sant Pau), C/ Sant Antoni Maria Claret, 167, Pavelló 18, planta 0, 08025 Barcelona, Spain.
authors.forename: Robin W M
authors.initials: RW
authors.lastname: Vernooij
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada; Institute of Health Policy, Management & Evaluation, University of Toronto, 4th Floor, 155 College St, Toronto, Ontario M5T 3M6, Canada; Department of Anesthesia & Pain Medicine, The Hospital for Sick Children, 555 University Ave., Toronto, Ontario M5G 1X8, Canada.
authors.forename: Brad C
authors.initials: BC
authors.lastname: Johnston
authors.affiliation: Chinese Evidence-based Medicine Center, West China Hospital, Sichuan University, 37 Guo Xue Xiang, Chengdu 610041, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Sun
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada; Basel Institute for Clinical Epidemiology and Biostatistics, Department of Clinical Research, University Hospital Basel, Spitalstrasse 12, 4031 Basel, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Briel
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada; Department of Anesthesia, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada; Michael G. DeGroote Institute for Pain Research and Care, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada.
authors.forename: Jason W
authors.initials: JW
authors.lastname: Busse
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada; Meta-Research Innovation Center at Stanford (METRICS), Stanford University, 1265 Welch Road, Stanford, CA 94305, USA.
authors.forename: Shanil
authors.initials: S
authors.lastname: Ebrahim
authors.affiliation: Área de investigaciones, Facultad de Medicina, Universidad de La Sabana, Campus del Puente del Común Km, 7 Autopista Norte, Chía, Colombia.
authors.forename: Carlos E
authors.initials: CE
authors.lastname: Granados
authors.affiliation: Department of Medicine, McMaster University, 1280 Main St W, Hamilton, Ontario L8S 4L8, Canada.
authors.forename: Alfonso
authors.initials: A
authors.lastname: Iorio
authors.affiliation: Department of Cardiology, University of Louisville, Rudd Heart & Lung Building, 201 Abraham Flexner Way, Suite 600, Louisville, KY 40292, USA.
authors.forename: Affan
authors.initials: A
authors.lastname: Irfan
authors.affiliation: Clinical Epidemiology and Public Health Department, Iberoamerican Cochrane Centre, Biomedical Research Institute Sant Pau (IIB Sant Pau), C/ Sant Antoni Maria Claret, 167, Pavelló 18, planta 0, 08025 Barcelona, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Martínez García
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada; Departments of Medicine and Biomedical & Health Informatics, University of Missouri-Kansas City, School of Medicine, M4-303, 2411 Holmes St, Kansas City, MO, USA.
authors.forename: Reem A
authors.initials: RA
authors.lastname: Mustafa
authors.affiliation: CCSS Permanent Medical Advisor, Health Care Development Division, IHCAI Foundation & Central America Cochrane, 1st Ave., 35th and 37th St, Number 3530, Barrio Escalante, San José, Costa Rica.
authors.forename: Anggie
authors.initials: A
authors.lastname: Ramírez-Morera
authors.affiliation: Clinical Epidemiology and Public Health Department, Iberoamerican Cochrane Centre, Biomedical Research Institute Sant Pau (IIB Sant Pau), C/ Sant Antoni Maria Claret, 167, Pavelló 18, planta 0, 08025 Barcelona, Spain.
authors.forename: Anna
authors.initials: A
authors.lastname: Selva
authors.affiliation: Clinical Epidemiology and Public Health Department, Iberoamerican Cochrane Centre, Biomedical Research Institute Sant Pau (IIB Sant Pau), C/ Sant Antoni Maria Claret, 167, Pavelló 18, planta 0, 08025 Barcelona, Spain.
authors.forename: Ivan
authors.initials: I
authors.lastname: Solà
authors.affiliation: Clinical Epidemiology and Public Health Department, Iberoamerican Cochrane Centre, Biomedical Research Institute Sant Pau (IIB Sant Pau), C/ Sant Antoni Maria Claret, 167, Pavelló 18, planta 0, 08025 Barcelona, Spain.
authors.forename: Andrea Juliana
authors.initials: AJ
authors.lastname: Sanabria
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada; Departments of Urology and Public Health, Helsinki University Hospital and University of Helsinki, Haartmaninkatu 4, 00029 Helsinki, Finland.
authors.forename: Kari A O
authors.initials: KA
authors.lastname: Tikkinen
authors.affiliation: Institute of Health and Society, Faculty of Medicine, University of Oslo, P.O. Box 1130 Blindern, 0318 Oslo, Norway; Guang'anmen Hospital China Academy of Chinese Medical Science, No. 5 Bei Xian Ge St, Xuan Wu District, Beijing 100053, China.
authors.forename: Per Olav
authors.initials: PO
authors.lastname: Vandvik
authors.affiliation: Clinical Epidemiology and Public Health Department, Iberoamerican Cochrane Centre, Biomedical Research Institute Sant Pau (IIB Sant Pau), C/ Sant Antoni Maria Claret, 167, Pavelló 18, planta 0, 08025 Barcelona, Spain.
authors.forename: Oscar E
authors.initials: OE
authors.lastname: Zazueta
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada; Guang'anmen Hospital China Academy of Chinese Medical Science, No. 5 Bei Xian Ge St, Xuan Wu District, Beijing 100053, China.
authors.forename: Yuqing
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada.
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhou
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada; Department of Medicine, McMaster University, 1280 Main St W, Hamilton, Ontario L8S 4L8, Canada.
authors.forename: Holger
authors.initials: H
authors.lastname: Schünemann
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada; Department of Medicine, McMaster University, 1280 Main St W, Hamilton, Ontario L8S 4L8, Canada.
authors.forename: Gordon H
authors.initials: GH
authors.lastname: Guyatt
mesh_terms: D003627:Data Interpretation, Statistical; D003695:Delivery of Health Care / Q000592:standards / Q000639:trends; D016021:Epidemiologic Studies; D006801:Humans; D016017:Odds Ratio; D063868:Patient Outcome Assessment; D011786:Quality Control; D012107:Research Design; D058028:Research Report
keywords: Absolute effect estimates; Absolute measures; Decision making; Framing; Reporting; Risk difference; Systematic review