title: A systematic review of individual patient data meta-analyses on surgical interventions.
abstract: BACKGROUND
  Compared to subgroup analyses in a single study or in a traditional meta-analysis, an individual patient data meta-analysis (IPDMA) offers important potential advantages. We studied how many IPDMAs report on surgical interventions, how many of those surgical IPDMAs perform subgroup analyses, and whether these subgroup analyses have changed decision-making in clinical practice.
  
  
  METHODS
  Surgical IPDMAs were identified using a comprehensive literature search. The last search was conducted on 24 April 2012. For each IPDMA included, we obtained information using a standardized data extraction form, and the quality of reporting was assessed. We also checked whether results were implemented in clinical guidelines.
  
  
  RESULTS
  Of all 583 identified IPDMAs, 22 (4%) reported on a surgical intervention. Eighteen (82%) of these IPDMAs presented subgroup analyses. Subgroups were mainly based on patient and disease characteristics. The median number of reported subgroup analyses was 3.5 (IQR 1.25-6.5). Statistical methods for subgroup analyses were mentioned in 11 (61%) surgical IPDMAs.Eleven (61%) of the 18 IPDMAs performing subgroup analyses reported a significant overall effect estimate, whereas six (33%) reported a non-significant one. Of the IPDMAs that reported non-significant overall results, three IPDMAs (50%) reported significant results in one or more subgroup analyses. Results remained significant in one or more subgroups in eight of the IPDMAs (73%) that reported a significant overall result.Eight (44%) of the 18 significant subgroups appeared to be implemented in clinical guidelines. The quality of reporting among surgical IPDMAs varied from low to high quality.
  
  
  CONCLUSIONS
  Many of the surgical IPDMAs performed subgroup analyses, but overall treatment effects were more often emphasized than subgroup effects. Although, most surgical IPDMAs included in the present study have only recently been published, about half of the significant subgroups were already implemented in treatment guidelines.
authors.affiliation: Department of Operating Rooms, Radboud University Nijmegen Medical Center, PO Box 9101, Nijmegen 6500HB, The Netherlands. g.hannink@orthop.umcn.nl
authors.forename: Gerjon
authors.initials: G
authors.lastname: Hannink
authors.forename: Hein G
authors.initials: HG
authors.lastname: Gooszen
authors.forename: Cornelis J H M
authors.initials: CJ
authors.lastname: van Laarhoven
authors.forename: Maroeska M
authors.initials: MM
authors.lastname: Rovers
mesh_terms: D003625:Data Collection / Q000379:methods*; D006801:Humans; D015201:Meta-Analysis as Topic; D012107:Research Design; D013514:Surgical Procedures, Operative