title: Cross-cultural validity of the thyroid-specific quality-of-life patient-reported outcome measure, ThyPRO.
abstract: OBJECTIVE
  Thyroid diseases are common and often affect quality of life (QoL). No cross-culturally validated patient-reported outcome measuring thyroid-related QoL is available. The purpose of the present study was to test the cross-cultural validity of the newly developed thyroid-related patient-reported outcome ThyPRO, using tests for differential item functioning (DIF) according to language version.
  
  
  METHODS
  The ThyPRO consists of 85 items summarized in 13 multi-item scales and one single item. Scales cover physical and mental symptoms, well-being and function as well as social and daily function and cosmetic concerns. Translation applied standard forward-backward methodology with subsequent cognitive interviews and reviews. Responses (N = 1,810) to the ThyPRO were collected in seven countries: UK (n = 166), The Netherlands (n = 147), Serbia (n = 150), Italy (n = 110), India (n = 148), Denmark (n = 902) and Sweden (n = 187). Translated versions were compared pairwise to the English version by examining uniform and nonuniform DIF, i.e., whether patients from different countries respond differently to a particular item, although they have identical level of the concept measured by the item. Analyses were controlled for thyroid diagnosis. DIF was investigated by ordinal logistic regression, testing for both statistical significance and magnitude (ΔR (2) > 0.02). Scale level was estimated by the sum score, after purification.
  
  
  RESULTS
  For twelve of the 84 tested items, DIF was identified in more than one language. Eight of these were small, but four were indicative of possible low translatability. Twenty-one instances of DIF in single languages were identified, indicating potential problems with the particular translation. However, only seven were of a magnitude which could affect scale scores, most of which could be explained by sample differences not controlled for.
  
  
  CONCLUSIONS
  The ThyPRO has good cross-cultural validity with only minor cross-cultural invariance and is recommended for use in international multicenter studies.
authors.affiliation: Department of Endocrinology, Copenhagen University Hospital Rigshospitalet, Blegdamsvej 9, 2100, Copenhagen Ø, Denmark, torquil.watt@regionh.dk.
authors.forename: Torquil
authors.initials: T
authors.lastname: Watt
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Barbesino
authors.forename: Jakob Bue
authors.initials: JB
authors.lastname: Bjorner
authors.forename: Steen Joop
authors.initials: SJ
authors.lastname: Bonnema
authors.forename: Branka
authors.initials: B
authors.lastname: Bukvic
authors.forename: Russell
authors.initials: R
authors.lastname: Drummond
authors.forename: Mogens
authors.initials: M
authors.lastname: Groenvold
authors.forename: Laszlo
authors.initials: L
authors.lastname: Hegedüs
authors.forename: Valeska
authors.initials: V
authors.lastname: Kantzer
authors.forename: Kathryn E
authors.initials: KE
authors.lastname: Lasch
authors.forename: Claudio
authors.initials: C
authors.lastname: Marcocci
authors.forename: Anjali
authors.initials: A
authors.lastname: Mishra
authors.forename: Romana
authors.initials: R
authors.lastname: Netea-Maier
authors.forename: Merel
authors.initials: M
authors.lastname: Ekker
authors.forename: Ivan
authors.initials: I
authors.lastname: Paunovic
authors.forename: Terence J
authors.initials: TJ
authors.lastname: Quinn
authors.forename: Åse Krogh
authors.initials: ÅK
authors.lastname: Rasmussen
authors.forename: Audrey
authors.initials: A
authors.lastname: Russell
authors.forename: Mayilvaganan
authors.initials: M
authors.lastname: Sabaretnam
authors.forename: Johannes
authors.initials: J
authors.lastname: Smit
authors.forename: Ove
authors.initials: O
authors.lastname: Törring
authors.forename: Vladan
authors.initials: V
authors.lastname: Zivaljevic
authors.forename: Ulla
authors.initials: U
authors.lastname: Feldt-Rasmussen
mesh_terms: D000328:Adult; D003431:Cross-Cultural Comparison; D003469:Culture; D003718:Denmark; D005260:Female; D006801:Humans; D007194:India; D007558:Italy; D007802:Language; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009426:Netherlands; D063868:Patient Outcome Assessment; D010549:Personal Satisfaction; D011788:Quality of Life / Q000523:psychology*; D057566:Self Report; D055771:Serbia; D011795:Surveys and Questionnaires; D013548:Sweden; D013959:Thyroid Diseases / Q000175:diagnosis / Q000628:therapy*; D014177:Translations