A 13-item Health of the Nation Outcome Scale (HoNOS 13): Validation by Item Response Theory (IRT) in people with Substance Use Disorder

Background: The Health of the Nation Outcome Scale (HoNOS) is a widely used 12-item tool to assess mental health and social functioning. The French version has an added 13 th item measuring adherence to psychotropic medication. The aim of the current study is to uncover the unknown pattern of item 13 and to compare the unidimensional and multi-dimensional fit of both the original HoNOS 12 and the new HoNOS 13 using Item Response Theory (IRT) modelling. This research question was studied among inpatients with substance use disorder (SUD). MethodsSix hundred and nine valid questionnaires of the HoNOS were analyzed using the multidimensional extension of the IRT graded-response modelling. For HoNOS 13, we fitted respectively a one-factor and a two-factor model. ResultsThe two-factor model suggesting a first factor capturing psychiatric/impairment-related issues and a second factor reflecting social-related issues yielded better goodness-of-fit values compared to the one-factor solution. ConclusionsWe were able to validate the 13-item questionnaire including medication compliance and suggest that the HoNOS 13 can be recommended as a clinical evaluation tool to assess the problems and treatment needs for inpatients with SUD. In IRT analyses, the items related to substance use and item 13 showed moderate discriminative abilities to catch the severity of the latent construct whereas the items related to the second factor (social problems) showed higher discriminative abilities. Trial registrationClinicalTrials.gov, Identifier: NCT03551301, registered: 11.06.2018.