title: Quality of life in European patients with Addison's disease: validity of the disease-specific questionnaire AddiQoL.
abstract: BACKGROUND
  Patients with Addison's disease (AD) self-report impairment in specific dimensions on well-being questionnaires. An AD-specific quality-of-life questionnaire (AddiQoL) was developed to aid evaluation of patients.
  
  
  OBJECTIVE
  We aimed to translate and determine construct validity, reliability, and concurrent validity of the AddiQoL questionnaire.
  
  
  METHODS
  After translation, the final versions were tested in AD patients from Norway (n = 107), Sweden (n = 101), Italy (n = 165), Germany (n = 200), and Poland (n = 50). Construct validity was examined by exploratory factor analysis and Rasch analysis, aiming at unidimensionality and fit to the Rasch model. Reliability was determined by Cronbach's coefficient-α and Person separation index. Longitudinal reliability was tested by differential item functioning in stable patient subgroups. Concurrent validity was examined in Norwegian (n = 101) and Swedish (n = 107) patients.
  
  
  RESULTS
  Exploratory factor analysis and Rasch analysis identified six items with poor psychometric properties. The 30 remaining items fitted the Rasch model and proved unidimensional, supported by appropriate item and person fit residuals and a nonsignificant χ(2) probability. Crohnbach's α-coefficient 0.93 and Person separation index 0.86 indicate high reliability. Longitudinal reliability was excellent. Correlation with Short Form-36 and Psychological General Well-Being Index scores was high. A shorter subscale comprising eight items also proved valid and reliable. Testing of AddiQoL-30 in this large patient cohort showed significantly worse scores with increasing age and in women compared with men but no difference between patients with isolated AD and those with concomitant diseases.
  
  
  CONCLUSIONS
  The validation process resulted in a revised 30-item AddiQoL questionnaire and an eight-item AddiQoL short version with good psychometric properties and high reliability.
authors.affiliation: Institute of Medicine, Haukeland University Hospital, Jonas Liesvei 65, N-5021 Bergen, Norway. marianne.oksnes@med.uib.no
authors.forename: Marianne
authors.initials: M
authors.lastname: Øksnes
authors.forename: Sophie
authors.initials: S
authors.lastname: Bensing
authors.forename: Anna-Lena
authors.initials: AL
authors.lastname: Hulting
authors.forename: Olle
authors.initials: O
authors.lastname: Kämpe
authors.forename: Annika
authors.initials: A
authors.lastname: Hackemann
authors.forename: Gesine
authors.initials: G
authors.lastname: Meyer
authors.forename: Klaus
authors.initials: K
authors.lastname: Badenhoop
authors.forename: Corrado
authors.initials: C
authors.lastname: Betterle
authors.forename: Anna
authors.initials: A
authors.lastname: Parolo
authors.forename: Roberta
authors.initials: R
authors.lastname: Giordano
authors.forename: Alberto
authors.initials: A
authors.lastname: Falorni
authors.forename: Lucyna
authors.initials: L
authors.lastname: Papierska
authors.forename: Wojciech
authors.initials: W
authors.lastname: Jeske
authors.forename: Anna A
authors.initials: AA
authors.lastname: Kasperlik-Zaluska
authors.forename: V Krishna K
authors.initials: VK
authors.lastname: Chatterjee
authors.forename: Eystein S
authors.initials: ES
authors.lastname: Husebye
authors.forename: Kristian
authors.initials: K
authors.lastname: Løvås
mesh_terms: D000224:Addison Disease / Q000175:diagnosis / Q000453:epidemiology* / Q000503:physiopathology / Q000523:psychology*; D000293:Adolescent; D000328:Adult; D000368:Aged; D005060:Europe; D005260:Female; D005858:Germany / Q000453:epidemiology; D006801:Humans; D007558:Italy / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D011044:Poland / Q000453:epidemiology; D011788:Quality of Life; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult