title: Assessing fibromyalgia-related fatigue: content validity and psychometric performance of the Fatigue Visual Analog Scale in adult patients with fibromyalgia.
abstract: OBJECTIVE
  To document 1) the content validity and 2) measure improvements in fatigue, using the Fatigue Visual Analogue Scale (VAS) assessment tool in patients with fibromyalgia.
  
  
  METHODS
  The relevance and comprehensiveness of the Fatigue VAS were tested through a qualitative analysis of 20 subjects' verbatim transcripts from semi-structured qualitative interviews. Data from two randomised, controller trials in fibromyalgia (n=1121) were used to conduct correlation analyses with the Fatigue and Tiredness items from the Fibromyalgia Impact Questionnaire (FIQ) and the Short Form-36 Vitality scale. Known-groups and cross classification analyses were conducted to demonstrate the ability to measure improvement in fatigue using the Fatigue VAS.
  
  
  RESULTS
  All subjects spontaneously reported that fatigue was an important symptom to capture in fibromyalgia. The Fatigue VAS was well understood by most subjects (n=18/20). High correlations (Pearson r>0.75) and good agreement (k>0.66) were found between the Fatigue VAS and the FIQ tiredness items no. 16 and 17 and SF-36™ Vitality scale. In both clinical trials there was a substantial separation of approximately 20 points on the mean change in the Fatigue VAS score between responders (>30% improvement in pain VAS) and non-responders.
  
  
  CONCLUSIONS
  Previous studies have confirmed that fatigue is a major component of the fibromyalgia experience. This current study reports that fibromyalgia patients spontaneously rated fatigue as a highly significant feature of their illness, and supports the use of the Fatigue VAS as a valid questionnaire in fibromyalgia clinical trials.
authors.affiliation: Mapi Values, Tokyo, Japan. bruce.crawford@mapivalues.com
authors.forename: B K
authors.initials: BK
authors.lastname: Crawford
authors.forename: E C
authors.initials: EC
authors.lastname: Piault
authors.forename: C
authors.initials: C
authors.lastname: Lai
authors.forename: R M
authors.initials: RM
authors.lastname: Bennett
mesh_terms: D000328:Adult; D000368:Aged; D000700:Analgesics / Q000627:therapeutic use; D059350:Chronic Pain / Q000175:diagnosis* / Q000188:drug therapy / Q000503:physiopathology / Q000523:psychology; D015673:Fatigue Syndrome, Chronic / Q000175:diagnosis* / Q000188:drug therapy / Q000503:physiopathology / Q000523:psychology; D005260:Female; D005356:Fibromyalgia / Q000175:diagnosis* / Q000188:drug therapy / Q000503:physiopathology / Q000523:psychology; D006304:Health Status; D006801:Humans; D007407:Interviews as Topic; D008297:Male; D008875:Middle Aged; D010147:Pain Measurement; D011594:Psychometrics / Q000379:methods*; D018434:Sickness Impact Profile; D012978:Sodium Oxybate / Q000627:therapeutic use; D013577:Syndrome
chemical_list: D000700:Analgesics; D012978:Sodium Oxybate