title: Does updating improve the methodological and reporting quality of systematic reviews?
abstract: BACKGROUND
  Systematic reviews (SRs) must be of high quality. The purpose of our research was to compare the methodological and reporting quality of original versus updated Cochrane SRs to determine whether updating had improved these two quality dimensions.
  
  
  METHODS
  We identified updated Cochrane SRs published in issue 4, 2002 of the Cochrane Library. We assessed the updated and original versions of the SRs using two instruments: the 10 item enhanced Overview Quality Assessment Questionnaire (OQAQ), and an 18-item reporting quality checklist and flow chart based upon the Quality of Reporting of Meta-analyses (QUOROM) statement. At least two reviewers extracted data and assessed quality. We calculated the percentage (with a 95% confidence interval) of 'yes' answers to each question. We calculated mean differences in percentage, 95% confidence intervals and p-values for each of the individual items and the overall methodological quality score of the updated and pre-updated versions using OQAQ.
  
  
  RESULTS
  We assessed 53 SRs. There was no significant improvement in the global quality score of the OQAQ (mean difference 0.11 (-0.28; 0.70 p = 0.52)). Updated reviews showed a significant improvement of 18.9 (7.2; 30.6 p < .01) on the OQAQ item assessing whether the conclusions drawn by the author(s) were supported by the data and/or analysis presented in the SR. The QUOROM statement showed that the quality of reporting of Cochrane reviews improved in some areas with updating. Improvements were seen on the items relating to data sources reported in the abstract, with a significant difference of 17.0 (9.8; 28.7 p = 0.01), review methods, reported in the abstract 35 (24.1; 49.1 p = 0.00), searching methods 18.9 (9.7; 31.6 p = 0.01), and data abstraction 18.9 (11.7; 30.9 p = 0.00).
  
  
  CONCLUSIONS
  The overall quality of Cochrane SRs is fair-to-good. Although reporting quality improved on certain individual items there was no overall improvement seen with updating and methodological quality remained unchanged. Further improvement of quality of reporting is possible. There is room for improvement of methodological quality as well. Authors updating reviews should address identified methodological or reporting weaknesses. We recommend to give full attention to both quality domains when updating SRs.
authors.affiliation: Community Information and Epidemiological Technologies (CIET), Ottawa, Ontario, Canada. bshea@ciet.org
authors.forename: Beverley
authors.initials: B
authors.lastname: Shea
authors.forename: Maarten
authors.initials: M
authors.lastname: Boers
authors.forename: Jeremy M
authors.initials: JM
authors.lastname: Grimshaw
authors.forename: Candyce
authors.initials: C
authors.lastname: Hamel
authors.forename: Lex M
authors.initials: LM
authors.lastname: Bouter
mesh_terms: D015706:Bibliometrics; D015201:Meta-Analysis as Topic; D017712:Peer Review, Research; D010506:Periodicals as Topic / Q000592:standards*; D011786:Quality Control; D012107:Research Design / Q000592:standards; D012196:Review Literature as Topic; D012985:Software Design