title: Impact of missing participant data for dichotomous outcomes on pooled effect estimates in systematic reviews: a protocol for a methodological study.
abstract: BACKGROUND
  There is no consensus on how authors conducting meta-analysis should deal with trial participants with missing outcome data. The objectives of this study are to assess in Cochrane and non-Cochrane systematic reviews: (1) which categories of trial participants the systematic review authors consider as having missing participant data (MPD), (2) how trialists reported on participants with missing outcome data in trials, (3) whether systematic reviewer authors actually dealt with MPD in their meta-analyses of dichotomous outcomes consistently with their reported methods, and (4) the impact of different methods of dealing with MPD on pooled effect estimates in meta-analyses of dichotomous outcomes.
  
  
  METHODS
  We will conduct a methodological study of Cochrane and non-Cochrane systematic reviews. Eligible systematic reviews will include a group-level meta-analysis of a patient-important dichotomous efficacy outcome, with a statistically significant effect estimate. Teams of two reviewers will determine eligibility and subsequently extract information from each eligible systematic review in duplicate and independently, using standardized, pre-piloted forms. The teams will then use a similar process to extract information from the trials included in the meta-analyses of interest. We will assess first which categories of trial participants the systematic reviewers consider as having MPD. Second, we will assess how trialists reported on participants with missing outcome data in trials. Third, we will compare what systematic reviewers report having done, and what they actually did, in dealing with MPD in their meta-analysis. Fourth, we will conduct imputation studies to assess the effects of different methods of dealing with MPD on the pooled effect estimates of meta-analyses. We will specifically calculate for each method (1) the percentage of systematic reviews that lose statistical significance and (2) the mean change of effect estimates across systematic reviews.
  
  
  CONCLUSIONS
  The impact of different methods of dealing with MPD on pooled effect estimates will help judge the associated risk of bias in systematic reviews. Our findings will inform recommendations regarding what assumptions for MPD should be used to test the robustness of meta-analytical results.
authors.affiliation: Department of Internal Medicine, Clinical Epidemiology Unit, American University of Beirut Medical Center, PO Box: 11-0236, Riad-El-Solh, Beirut 1107, 2020, Beirut, Lebanon. ea32@aub.edu.lb.
authors.forename: Elie A
authors.initials: EA
authors.lastname: Akl
authors.forename: Lara A
authors.initials: LA
authors.lastname: Kahale
authors.forename: Arnav
authors.initials: A
authors.lastname: Agarwal
authors.forename: Nada
authors.initials: N
authors.lastname: Al-Matari
authors.forename: Shanil
authors.initials: S
authors.lastname: Ebrahim
authors.forename: Paul Elias
authors.initials: PE
authors.lastname: Alexander
authors.forename: Matthias
authors.initials: M
authors.lastname: Briel
authors.forename: Romina
authors.initials: R
authors.lastname: Brignardello-Petersen
authors.forename: Jason W
authors.initials: JW
authors.lastname: Busse
authors.forename: Batoul
authors.initials: B
authors.lastname: Diab
authors.forename: Alfonso
authors.initials: A
authors.lastname: Iorio
authors.forename: Joey
authors.initials: J
authors.lastname: Kwong
authors.forename: Ling
authors.initials: L
authors.lastname: Li
authors.forename: Luciane Cruz
authors.initials: LC
authors.lastname: Lopes
authors.forename: Reem
authors.initials: R
authors.lastname: Mustafa
authors.forename: Ignacio
authors.initials: I
authors.lastname: Neumann
authors.forename: Kari A O
authors.initials: KA
authors.lastname: Tikkinen
authors.forename: Per Olav
authors.initials: PO
authors.lastname: Vandvik
authors.forename: Yuqing
authors.initials: Y
authors.lastname: Zhang
authors.forename: Pablo
authors.initials: P
authors.lastname: Alonso-Coello
authors.forename: Gordon
authors.initials: G
authors.lastname: Guyatt
mesh_terms: D015982:Bias; D015201:Meta-Analysis as Topic; D000078202:Systematic Reviews as Topic