The GRADE working group has recently adopted guidance for assessing the risk of bias associated with missing participant outcome data across an entire body of evidence. This post summarizes the guidance, provides a background, relevant references, and links to excel documents with calculators to facilitate the use of the guidance.
· Start with a primary meta-analysis using a complete case analysis (i.e., excluding those with missing data)
· Then conduct sensitivity meta-analyses imputing, in each study, data for those with missing data, and then pooling across studies.
o For binary outcomes: we suggest use of “plausible worst case” in which review authors assume that those with missing data in treatment arms have proportionally higher event rates than those followed successfully.
o For continuous outcomes: use imputed mean values from other studies within the systematic review, and the standard deviation from the median standard deviations of the control arms of all studies. For meta-analyses in which investigators have used different instruments to address the same construct, convert all scores to standardized mean difference (SMD) or to the units of a selected reference instrument.
· If the results of the primary meta-analysis are robust to the most extreme plausible assumptions, do not rate down quality of evidence for risk of bias due to missing participant outcome data.
· If the results of the primary meta-analysis are not robust to the most extreme plausible assumptions, consider rating down quality for risk of bias.
Links to MPD assumptions calculators
Binary variables: A freely downloadable Excel document to determine the numerators and denominators to be used for each trial included in the metaanalysis according to the selected assumption: https://www.dropbox.com/s/opstwgm45qiq57k/Assumptions%20about%20MPD%20v5.xls?dl=0
Continuous variables: A freely downloadable Excel document to determine the means and SDs to be used for each trial included in the meta-analysis according to the selected assumption per strategy: