Background: Primary study selection between systematic reviews is inconsistent, and reviews on the same topic may reach different conclusions. Our main objective was to compare systematic reviews on negative pressure wound therapy (NPWT) regarding their agreement in primary study selection.
Methods: This retrospective analysis was conducted within the framework of a systematic review (a full review and a subsequent rapid report) on NPWT prepared by the Institute for Quality and Efficiency in Health Care (IQWiG). For the IQWiG review and rapid report, 4 bibliographic databases (MEDLINE, EMBASE, The Cochrane Library, and CINAHL) were searched to identify systematic reviews and primary studies on NPWT versus conventional wound therapy in patients with acute or chronic wounds. All databases were searched from inception to December 2006. For the present analysis, reviews on NPWT were classified as eligible systematic reviews if multiple sources were systematically searched and the search strategy was documented. To ensure comparability between reviews, only reviews published in or after December 2004 and only studies published before June 2004 were considered. Eligible reviews were compared in respect of the methodology applied and the selection of primary studies.
Results: A total of 5 systematic reviews (including the IQWiG review) and 16 primary studies were analysed. The reviews included between 4 and 13 primary studies published before June 2004. Two reviews considered only randomised controlled trials (RCTs). Three reviews considered both RCTs and non-RCTs. The overall agreement in study selection between reviews was 96% for RCTs (24 of 25 options) and 57% for non-RCTs (12 of 21 options). Due to considerable disagreement in the citation and selection of non-RCTs, we contacted the review authors for clarification (this was not initially planned); all authors or institutions responded. According to published information and the additional information provided, most differences between reviews arose from variations in inclusion criteria or inter-author study classification, as well as from different reporting styles (citation or non-citation) for excluded studies.
Conclusion: The citation and selection of primary studies differ between systematic reviews on NPWT, particularly with regard to non-RCTs. Uniform methodological and reporting standards need to be applied to ensure comparability between reviews as well as the validity of their conclusions.