title: Reliability and validity of the Bowel Function Index for evaluating opioid-induced constipation: translation, cultural adaptation and validation of the Portuguese version (BFI-P).
abstract: The Bowel Function Index (BFI) is a simple and sound bowel function and opioid-induced constipation (OIC) screening tool. We aimed to develop the translation and cultural adaptation of this measure (BFI-P) and to assess its reliability and validity for the Portuguese language and a chronic pain population.
  
  
  
  The BFI-P was created after a process including translation, back translation and cultural adaptation. Participants (n = 226) were recruited in a chronic pain clinic and were assessed at baseline and after one week. Internal consistency, test-retest reliability, responsiveness, construct (convergent and known groups) and factorial validity were assessed.
  
  
  
  Test-retest reliability had an intra-class correlation of 0.605 for BFI mean score. Internal consistency of BFI had Cronbach's alpha of 0.865. The construct validity of BFI-P was shown to be excellent and the exploratory factor analysis confirmed its unidimensional structure. The responsiveness of BFI-P was excellent, with a suggested 17-19 point and 8-12 point change in score constituting a clinically relevant change in constipation for patients with and without previous constipation, respectively.
  
  
  
  This study had some limitations, namely, the criterion validity of BFI-P was not directly assessed; and the absence of a direct criterion for OIC precluded the assessment of the criterion based responsiveness of BFI-P. Nevertheless, BFI may importantly contribute to better OIC screening and its Portuguese version (BFI-P) has been shown to have excellent reliability, internal consistency, validity and responsiveness. Further suggestions regarding statistically and clinically important change cut-offs for this instrument are presented.
authors.affiliation: a Salus Infirmorum Faculty of Nursing , University of Cádiz , Cádiz , Spain.|b The Observatory of Pain (External Chair of Pain) , University of Cádiz , Cádiz , Spain.
authors.forename: María
authors.initials: M
authors.lastname: Dueñas
authors.affiliation: c Centro Nacional de Observação em Dor - OBSERVDOR (National Observatory for Pain - NOPain) , Portugal.
authors.forename: Liliane
authors.initials: L
authors.lastname: Mendonça
authors.affiliation: d Department of Experimental Biology, Faculty of Medicine , University of Porto , Portugal.|e IBMC - Institute for Molecular and Cell Biology, University of Porto , Portugal.
authors.forename: Rute
authors.initials: R
authors.lastname: Sampaio
authors.affiliation: d Department of Experimental Biology, Faculty of Medicine , University of Porto , Portugal.
authors.forename: Cláudia
authors.initials: C
authors.lastname: Gouvinhas
authors.affiliation: d Department of Experimental Biology, Faculty of Medicine , University of Porto , Portugal.
authors.forename: Daniela
authors.initials: D
authors.lastname: Oliveira
authors.affiliation: c Centro Nacional de Observação em Dor - OBSERVDOR (National Observatory for Pain - NOPain) , Portugal.|d Department of Experimental Biology, Faculty of Medicine , University of Porto , Portugal.|e IBMC - Institute for Molecular and Cell Biology, University of Porto , Portugal.
authors.forename: José Manuel
authors.initials: JM
authors.lastname: Castro-Lopes
authors.affiliation: c Centro Nacional de Observação em Dor - OBSERVDOR (National Observatory for Pain - NOPain) , Portugal.|f Department of Health Information and Decision Sciences (CIDES), Faculty of Medicine , University of Porto , Portugal.|g CINTESIS - Centre for Health Technology and Services Research, University of Porto , Portugal.
authors.forename: Luís Filipe
authors.initials: LF
authors.lastname: Azevedo
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000701:Analgesics, Opioid / Q000009:adverse effects*; D059350:Chronic Pain / Q000188:drug therapy*; D003248:Constipation / Q000139:chemically induced*; D003672:Defecation / Q000187:drug effects*; D005260:Female; D006801:Humans; D007802:Language; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results
chemical_list: D000701:Analgesics, Opioid
keywords: Bowel function; chronic pain; factor analysis; opioid-induced constipation; reliability; responsiveness; validity