title: Adjustment for compliance behavior in trials of epidural analgesia in labor using instrumental variable meta-analysis.
abstract: OBJECTIVE
  Intention-to-treat (ITT) analysis of randomized controlled trials (RCTs) may cause bias when compliance is poor. Noncompliance describes failure to comply with allocation in the intervention arm, and contamination describes uptake of the intervention in the control arm. Instrumental variable (IV) analysis can be applied in addition to the primary ITT analysis to estimate the causal effect adjusted for noncompliance and contamination, assuming that noncompliers would have had the same treatment benefit as compliers. We aimed to compare ITT and IV meta-analysis of the association between epidural analgesia in labor and cesarean section.
  
  
  METHODS
  The study was restricted to 27 trials in a Cochrane Systematic Review. The association between epidural analgesia in labor and cesarean section was calculated using ITT and IV analyses. Pooled risk ratios (RRs) were calculated using fixed-effects meta-analysis.
  
  
  RESULTS
  In 18 trials with compliance data, noncompliance was 23% and contamination was 27%. In 10 trials with outcome data stratified by compliance, the pooled RR for cesarean section following epidural analgesia was 1.37 [95% confidence interval (CI): 1.00, 1.89; P = 0.049] using IV compared with 1.19 (95% CI: 0.93, 1.51; P = 0.16) using ITT.
  
  
  CONCLUSIONS
  ITT meta-analysis underestimates the effect of receiving epidural analgesia in labor on cesarean section compared with IV meta-analysis.
authors.affiliation: Clinical and Population Perinatal Health Research, Kolling Institute of Medical Research, Building 52, University of Sydney at Royal North Shore Hospital, St Leonards 2065, New South Wales, Australia. Electronic address: melanie.bt@gmail.com.
authors.forename: Melanie
authors.initials: M
authors.lastname: Bannister-Tyrrell
authors.affiliation: Centre for Evidence Based Medicine, Morsani College of Medicine, University of South Florida, 3515 East Fletcher Avenue, MDT 1201, Tampa, FL 33612, USA.
authors.forename: Branko
authors.initials: B
authors.lastname: Miladinovic
authors.affiliation: Clinical and Population Perinatal Health Research, Kolling Institute of Medical Research, Building 52, University of Sydney at Royal North Shore Hospital, St Leonards 2065, New South Wales, Australia.
authors.forename: Christine L
authors.initials: CL
authors.lastname: Roberts
authors.affiliation: Clinical and Population Perinatal Health Research, Kolling Institute of Medical Research, Building 52, University of Sydney at Royal North Shore Hospital, St Leonards 2065, New South Wales, Australia.
authors.forename: Jane B
authors.initials: JB
authors.lastname: Ford
mesh_terms: D015360:Analgesia, Epidural; D016362:Analgesia, Obstetrical; D002585:Cesarean Section / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D057194:Intention to Treat Analysis; D007743:Labor, Obstetric; D010349:Patient Compliance; D011247:Pregnancy; D016032:Randomized Controlled Trials as Topic / Q000592:standards; D012107:Research Design
keywords: Cesarean section; Epidural analgesia; Instrumental variables; Intention-to-treat; Noncompliance; Randomized controlled trials