title: Value of updating a systematic review in surgery using individual patient data.
abstract: BACKGROUND
  Previous research has highlighted the advantages of individual patient data (IPD) meta-analyses. However, they are resource intensive and take considerable time to complete. The aim of this study was to determine whether the extra investment is justified by greater accuracy or usefulness by means of a case study in surgery.
  
  
  METHODS
  An updated review using IPD, where possible, was compared with an earlier version based on aggregate published data to determine whether there were statistically significant changes in estimates of effectiveness for hernia recurrence and persisting pain. Differences related to the type of laparoscopic repair, the type of open repair and methodological quality were also explored.
  
  
  RESULTS
  The results for hernia recurrence changed little. However, the IPD update led to divergent conclusions for persisting pain. The published data implied a statistically significant benefit in favour of open repair, whereas the IPD result implied a statistically significant benefit in favour of laparoscopic repair (P < 0.001). Methodological quality did not account for this difference.
  
  
  CONCLUSIONS
  Updating of systematic reviews using IPD can be conducted successfully in surgery. This example led to little change in estimates of effectiveness for hernia recurrence but yielded qualitatively different estimates for persisting pain, an outcome rarely included in the published reports.
authors.affiliation: Health Services Research Unit, University of Aberdeen, Polwarth Building, Foresterhill, Aberdeen AB25 2ZD, UK. k.mcCormack@abdn.ac.uk
authors.forename: K
authors.initials: K
authors.lastname: McCormack
authors.forename: A
authors.initials: A
authors.lastname: Grant
authors.forename: N
authors.initials: N
authors.lastname: Scott
mesh_terms: D006801:Humans; D003625:Data Collection / Q000379:methods; D006552:Hernia, Inguinal / Q000601:surgery; D008499:Medical Records; D015201:Meta-Analysis as Topic; D016017:Odds Ratio; D010149:Postoperative Pain / Q000209:etiology; D016032:Randomized Controlled Trials as Topic; D012008:Recurrence; D016896:Treatment Outcome; D000078202:Systematic Reviews as Topic