title: Quality scores do not predict discrepant statistical significances among meta-analyses on different targets of glycemic control in type 2 diabetes.
abstract: OBJECTIVE
  To examine differences in conclusions, statistical significances, and quality of systematic reviews on preventive effects of different targets of blood glucose lowering on macrovascular events in patients with type 2 diabetes.
  
  
  METHODS
  We searched MEDLINE, the Cochrane Database of Systematic Reviews, and Embase until October 15, 2011. Systematic reviews using meta-analyses to compare macrovascular events in patients with type 2 diabetes randomized to different therapeutic targets of blood glucose were eligible for inclusion in this study. Effect measures were extracted and quality was assessed by Overview Quality Assessment Questionnaire, Assessment of Multiple Systematic Reviews, and Preferred Reporting Items for Systematic Reviews and Meta-Analyses. An additional checklist was used to control for completeness and suitability of included trials, correctness of data extraction, and choice of outcome parameters.
  
  
  RESULTS
  The 16 included systematic reviews were partially discrepant in statistical significances of reported outcome parameters. Twelve systematic reviews did not include available relevant trials and included eight systematic reviews that should not have been included according to the systematic review's aim and search strategies. Quality differed considerably among systematic reviews.
  
  
  CONCLUSIONS
  Physicians, researchers, and policy makers should bear in mind that common quality assessment instruments are necessary but not sufficient to guarantee reliable results and conclusions obtained from meta-analyses.
authors.affiliation: Institute of Health Economics and Clinical Epidemiology, The University Hospital of Cologne (AöR), Gleueler Straße 167-178, 50935 Cologne, Germany. Electronic address: ampasson@googlemail.com.
authors.forename: Anna M
authors.initials: AM
authors.lastname: Passon
authors.forename: Anna
authors.initials: A
authors.lastname: Drabik
authors.forename: Peter T
authors.initials: PT
authors.lastname: Sawicki
mesh_terms: D015982:Bias; D001786:Blood Glucose / Q000032:analysis*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000517:prevention & control*; D006801:Humans; D012107:Research Design / Q000592:standards*
chemical_list: D001786:Blood Glucose
keywords: Glucose control; Meta-Analysis; Methodological quality; Systematic review; Type 2 diabetes; Vascular diseases