title: Systematic reviews with language restrictions and no author contact have lower overall credibility: a methodology study.
abstract: BACKGROUND
  High-quality systematic reviews (SRs) require rigorous approaches to identify, appraise, select, and synthesize research evidence relevant to a specific question. In this study, we evaluated the association between two steps in the conduct of an SR - restricting the search to English, and author contact for missing data - and the overall credibility of a SR.
  
  
  METHODS
  All SRs cited by the Endocrine Society's Clinical Practice Guidelines published from October 2006 through January 2012 were included. The main outcome was the overall A Measurement Tool to Assess Systematic Reviews (AMSTAR) score, as a surrogate of SR credibility. Nonparametric Kruskal-Wallis tests and multivariable linear regression models were used to investigate the association between language restriction, author contact for missing data, and the overall AMSTAR score.
  
  
  RESULTS
  In all, 69 SRs were included in the analysis. Only 31 SRs (45%) reported searching non-English literature, with an average AMSTAR score of 7.90 (standard deviation [SD] =1.64). SRs that reported language restriction received significantly lower AMSTAR scores (mean =5.25, SD =2.32) (P<0.001). Only 30 SRs (43%) reported contacting authors for missing data, and these received, on average, 2.59 more AMSTAR points (SD =1.95) than those who did not (P<0.001). In multivariable analyses, AMSTAR score was significantly correlated with language restriction (beta =-1.31, 95% confidence interval [CI]: -2.62, -0.01, P=0.05) and author contact for missing data (beta =2.16, 95% CI: 0.91, 3.41, P=0.001). However, after adjusting for compliance with reporting guidelines, language restriction was no longer significantly associated with the AMSTAR score.
  
  
  CONCLUSIONS
  Fewer than half of the SRs conducted to support the clinical practice guidelines we examined reported contacting study authors or searched non-English literature. SRs that did not conduct these two steps had lower quality scores, suggesting the importance of these two steps for overall SR credibility.
authors: Robert D and Patricia E Kern Center for the Science of Health Care Delivery, Mayo Clinic, Rochester, MN, USA ; Division of Health Care Policy and Research, Department of Health Sciences Research, Mayo Clinic, Rochester, MN, USA ; Knowledge and Evaluation Research Unit, Mayo Clinic, Rochester, MN, USA.
authors: Zhen
authors: Z
authors: Wang
authors: Division of Endocrinology, Diabetes, Metabolism, and Nutrition, Mayo Clinic, Rochester, MN, USA.
authors: Juan P
authors: JP
authors: Brito
authors: Aristotle University of Thessaloniki, Thessaloniki, Greece.
authors: Apostolos
authors: A
authors: Tsapas
authors: Division of Endocrinology, Diabetes, Metabolism, and Nutrition, Mayo Clinic, Rochester, MN, USA.
authors: Marcio L
authors: ML
authors: Griebeler
authors: Robert D and Patricia E Kern Center for the Science of Health Care Delivery, Mayo Clinic, Rochester, MN, USA ; Knowledge and Evaluation Research Unit, Mayo Clinic, Rochester, MN, USA.
authors: Fares
authors: F
authors: Alahdab
authors: Robert D and Patricia E Kern Center for the Science of Health Care Delivery, Mayo Clinic, Rochester, MN, USA ; Knowledge and Evaluation Research Unit, Mayo Clinic, Rochester, MN, USA ; Division of Preventive, Occupational and Aerospace Medicine, Mayo Clinic, Rochester, MN, USA.
authors: Mohammad Hassan
authors: MH
authors: Murad
keywords: evidence-based medicine; quality of evidence; research design; validity