Several reasons explained the variation in the results of 22 meta-analyses addressing the same question

OBJECTIVE: The objective of this study was to assess and to investigate the reasons for the variations between the results of meta-analyses addressing the same question. STUDY DESIGN AND SETTING: We included systematic reviews, and the trials that they included, on the use of implantable cardiac defibrillator (ICD) in patients with nonischemic cardiomyopathy. We assessed the variation between meta-analyses pooled effect estimates by calculating the percentage of absolute difference. We developed a list of 10 reasons for variations between the results of the meta-analyses clustered in four overarching categories. RESULTS: We identified 21 systematic reviews including six trials and reporting on 22 eligible meta-analyses. The percentage of absolute difference between each of the 22 pooled effect estimates (included odds ratio, risk ratio, hazard ratio) and their median value had an average of 3.2%. The number of trials for which the following categories of reasons for variations applied were as follows: (1) different decision to include or exclude trials (n = 3); (2) differences in analytical approaches (n = 6); (3) errors in conducting meta-analyses (n = 5); and (4) unclear reason (n = 1). CONCLUSION: Few of the observed variations between the results of the 22 meta-analyses could lead clinicians or guideline development organizations to adopt different courses of actions. Variations were most frequently related to both errors and variations in trial eligibility and analytical approaches.