title: Defining a minimal clinically important difference for endometriosis-associated pelvic pain measured on a visual analog scale: analyses of two placebo-controlled, randomized trials.
abstract: BACKGROUND
  When comparing active treatments, a non-inferiority (or one-sided equivalence) study design is often used. This design requires the definition of a non-inferiority margin, the threshold value of clinical relevance. In recent studies, a non-inferiority margin of 15 mm has been used for the change in endometriosis-associated pelvic pain (EAPP) on a visual analog scale (VAS). However, this value was derived from other chronic painful conditions and its validation in EAPP was lacking.
  
  
  METHODS
  Data were analyzed from two placebo-controlled studies of active treatments in endometriosis, including 281 patients with laparoscopically-confirmed endometriosis and moderate-to-severe EAPP. Patients recorded EAPP on a VAS at baseline and the end of treatment. Patients also assessed their satisfaction with treatment on a modified Clinical Global Impression scale. Changes in VAS score were compared with patients' self-assessments to derive an empirically validated non-inferiority margin. This anchor-based value was compared to a non-inferiority margin derived using the conventional half standard deviation rule for minimal clinically important difference (MCID) in patient-reported outcomes.
  
  
  RESULTS
  Anchor-based and distribution-based MCIDs were-7.8 mm and-8.6 mm, respectively.
  
  
  CONCLUSIONS
  An empirically validated non-inferiority margin of 10 mm for EAPP measured on a VAS is appropriate to compare treatments in endometriosis.
authors.affiliation: Global Clinical Statistics, Bayer Schering Pharma AG, 13342 Berlin, Germany. christoph.gerlinger@bayer.com
authors.forename: Christoph
authors.initials: C
authors.lastname: Gerlinger
authors.forename: Ulrike
authors.initials: U
authors.lastname: Schumacher
authors.forename: Thomas
authors.initials: T
authors.lastname: Faustmann
authors.forename: Antje
authors.initials: A
authors.lastname: Colligs
authors.forename: Heinz
authors.initials: H
authors.lastname: Schmitz
authors.forename: Christian
authors.initials: C
authors.lastname: Seitz
mesh_terms: D000293:Adolescent; D000328:Adult; D004715:Endometriosis / Q000150:complications* / Q000628:therapy; D005260:Female; D006801:Humans; D010535:Laparoscopy; D008875:Middle Aged; D010147:Pain Measurement / Q000379:methods*; D017060:Patient Satisfaction; D017699:Pelvic Pain / Q000503:physiopathology* / Q000523:psychology; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D055815:Young Adult