title: Reporting, handling and assessing the risk of bias associated with missing participant data in systematic reviews: a methodological survey.
abstract: OBJECTIVE
  To describe how systematic reviewers are reporting missing data for dichotomous outcomes, handling them in the analysis and assessing the risk of associated bias.
  
  
  METHODS
  We searched MEDLINE and the Cochrane Database of Systematic Reviews for systematic reviews of randomised trials published in 2010, and reporting a meta-analysis of a dichotomous outcome. We randomly selected 98 Cochrane and 104 non-Cochrane systematic reviews. Teams of 2 reviewers selected eligible studies and abstracted data independently and in duplicate using standardised, piloted forms with accompanying instructions. We conducted regression analyses to explore factors associated with using complete case analysis and with judging the risk of bias associated with missing participant data.
  
  
  RESULTS
  Of Cochrane and non-Cochrane reviews, 47% and 7% (p<0.0001), respectively, reported on the number of participants with missing data, and 41% and 9% reported a plan for handling missing categorical data. The 2 most reported approaches for handling missing data were complete case analysis (8.5%, out of the 202 reviews) and assuming no participants with missing data had the event (4%). The use of complete case analysis was associated only with Cochrane reviews (relative to non-Cochrane: OR=7.25; 95% CI 1.58 to 33.3, p=0.01). 65% of reviews assessed risk of bias associated with missing data; this was associated with Cochrane reviews (relative to non-Cochrane: OR=6.63; 95% CI 2.50 to 17.57, p=0.0001), and the use of the Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology (OR=5.02; 95% CI 1.02 to 24.75, p=0.047).
  
  
  CONCLUSIONS
  Though Cochrane reviews are somewhat less problematic, most Cochrane and non-Cochrane systematic reviews fail to adequately report and handle missing data, potentially resulting in misleading judgements regarding risk of bias.
authors.affiliation: Department of Internal Medicine, American University of Beirut, Beirut, Lebanon Department of Clinical Epidemiology & Biostatistics, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Elie A
authors.initials: EA
authors.lastname: Akl
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, Hamilton, Ontario, Canada Evidence Based Dentistry Unit, Faculty of Dentistry, Universidad de Chile, Santiago, Chile.
authors.forename: Alonso
authors.initials: A
authors.lastname: Carrasco-Labra
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, Hamilton, Ontario, Canada Evidence Based Dentistry Unit, Faculty of Dentistry, Universidad de Chile, Santiago, Chile Institute of Health Policy, Management & Evaluation, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Romina
authors.initials: R
authors.lastname: Brignardello-Petersen
authors.affiliation: Department of Medicine, Pontificia Universidad Católica de Chile, Santiago, Chile.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Neumann
authors.affiliation: Institute of Health Policy, Management & Evaluation, University of Toronto, Toronto, Ontario, Canada Department of Anesthesia & Pain Medicine, The Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: Bradley C
authors.initials: BC
authors.lastname: Johnston
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, Hamilton, Ontario, Canada Clinical Research and Evaluation Unit, Chinese Evidence-based Medicine Center, West China Hospital, Sichuan University, Chengdu, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Sun
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, Hamilton, Ontario, Canada Department of Clinical Research, Basel Institute for Clinical Epidemiology and Biostatistics, University Hospital Basel, Basel, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Briel
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, Hamilton, Ontario, Canada Department of Anesthesia, McMaster University, Hamilton, Ontario, Canada The Michael G. DeGroote Institute for Pain Research and Care, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Jason W
authors.initials: JW
authors.lastname: Busse
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, Hamilton, Ontario, Canada Department of Anesthesia, McMaster University, Hamilton, Ontario, Canada Department of Medicine, Stanford Prevention Research Center, Stanford University, Palo Alto, California, USA.
authors.forename: Shanil
authors.initials: S
authors.lastname: Ebrahim
authors.affiliation: Área de investigaciones, Facultad de Medicina, Universidad de La Sabana, Chía, Colombia.
authors.forename: Carlos E
authors.initials: CE
authors.lastname: Granados
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, Hamilton, Ontario, Canada Department of Medicine, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Alfonso
authors.identifier: http://orcid.org/0000-0002-3331-8766
authors.initials: A
authors.lastname: Iorio
authors.affiliation: Department of Cardiology, University of Louisville, Louisville, Kentucky, USA.
authors.forename: Affan
authors.initials: A
authors.lastname: Irfan
authors.affiliation: Iberoamerican Cochrane Centre, Biomedical Research Institute Sant Pau-CIBER of Epidemiology and Public Health (CIBERESP- IIB Sant Pau), Barcelona, Spain.
authors.forename: Laura
authors.initials: L
authors.lastname: Martínez García
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, Hamilton, Ontario, Canada Departments of Medicine, Nephrology and Biomedical and Health Informatics, University of Missouri-Kansas City, Kansas City, Missouri, USA.
authors.forename: Reem A
authors.initials: RA
authors.lastname: Mustafa
authors.affiliation: Health Care Development Division, IHCAI Foundation & Central America Cochrane, San José, Costa Rica.
authors.forename: Anggie
authors.initials: A
authors.lastname: Ramírez-Morera
authors.affiliation: Iberoamerican Cochrane Centre, Biomedical Research Institute Sant Pau-CIBER of Epidemiology and Public Health (CIBERESP- IIB Sant Pau), Barcelona, Spain.
authors.forename: Anna
authors.initials: A
authors.lastname: Selva
authors.affiliation: Iberoamerican Cochrane Centre, Biomedical Research Institute Sant Pau-CIBER of Epidemiology and Public Health (CIBERESP- IIB Sant Pau), Barcelona, Spain.
authors.forename: Ivan
authors.initials: I
authors.lastname: Solà
authors.affiliation: Iberoamerican Cochrane Centre, Biomedical Research Institute Sant Pau-CIBER of Epidemiology and Public Health (CIBERESP- IIB Sant Pau), Barcelona, Spain.
authors.forename: Andrea Juliana
authors.initials: AJ
authors.lastname: Sanabria
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, Hamilton, Ontario, Canada Departments of Urology and Public Health, Helsinki University Central Hospital and University of Helsinki, Helsinki, Finland.
authors.forename: Kari A O
authors.initials: KA
authors.lastname: Tikkinen
authors.affiliation: Norwegian Knowledge Centre for the Health Services, Oslo, Norway Department of Medicine, Innlandet Hospital Trust, Gjøvik, Norway.
authors.forename: Per O
authors.initials: PO
authors.lastname: Vandvik
authors.affiliation: Iberoamerican Cochrane Centre, Biomedical Research Institute Sant Pau-CIBER of Epidemiology and Public Health (CIBERESP- IIB Sant Pau), Barcelona, Spain.
authors.forename: Robin W M
authors.initials: RW
authors.lastname: Vernooij
authors.affiliation: Iberoamerican Cochrane Centre, Biomedical Research Institute Sant Pau-CIBER of Epidemiology and Public Health (CIBERESP- IIB Sant Pau), Barcelona, Spain.
authors.forename: Oscar E
authors.initials: OE
authors.lastname: Zazueta
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhou
authors.affiliation: Department of Clinical Epidemiology & Biostatistics, McMaster University, Hamilton, Ontario, Canada Department of Medicine, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Gordon H
authors.initials: GH
authors.lastname: Guyatt
authors.affiliation: Iberoamerican Cochrane Centre, Biomedical Research Institute Sant Pau-CIBER of Epidemiology and Public Health (CIBERESP- IIB Sant Pau), Barcelona, Spain.
authors.forename: Pablo
authors.initials: P
authors.lastname: Alonso-Coello
mesh_terms: D015982:Bias; D000068598:Data Accuracy; D006801:Humans; D015201:Meta-Analysis as Topic; D012107:Research Design / Q000592:standards; D012196:Review Literature as Topic; D011795:Surveys and Questionnaires
keywords: EPIDEMIOLOGY; STATISTICS & RESEARCH METHODS