The Practical and Social Functioning (PSF) scale: development and measurement properties of an instrument for assessing activity and social participation among people with serious mental illness.

Background: Participation in society and the ability to perform various activities are crucial aspects of everyday functioning. The intertwined relationship between functioning, disability, and health is emphasized in the "International Classification of Functioning, Disability and Health (ICF)" framework. In recent decades, mental health care units have increasingly focused on this aspect. The Practical and Social Functioning scale (PSF) was developed and validated in Norwegian as an easy-to-administer instrument to assess practical and social functioning among patients with serious mental illness in different clinical settings.

Methods: The PSF was developed and revised using data from different Norwegian studies. Data from a total of 562 patients with serious mental illness in different clinical settings were included. The validation process included the evaluation of items into categories by 25 professionals. Development and revision took place in three different stages, and factor analyses were conducted. The quality of the PSF was assessed according to the COSMIN standards for systematic reviews on patient-reported outcome measures.

Results: The final version of the PSF comprises seven subscales, each consisting of four items, resulting in a total of 28 items. These subscales, along with their corresponding items, are loaded onto two factors representing the main dimensions of functioning: activity and participation. Content validity comprises three domains: relevance, comprehensiveness, and comprehensibility. Relevance and comprehensibility were found to be adequate, whereas comprehensiveness was doubtful. Structural validity was adequate, internal consistency was very good, and construct validity was adequate compared to the Global Assessment of Functioning scale. Responsiveness was found to be doubtful in our study with data from an 18-month observation period. Nearly 60% of the items showed a ceiling effect. No items showed a floor effect.

Conclusion: The development and validation of the Norwegian version of the PSF resulted in an instrument consisting of seven subscales and a total of 28 items. The items and subscales assess functioning related to two key factors according to the ICF framework: activity and participation. Our results show that the PSF is an easy-to-administer instrument that may be particularly sensitive for detecting variation among persons with severely impaired functioning.

Trial Registration: The study Implementation of Guidelines for the Treatment of Psychoses was registered retrospectively on 31 August 2017 at ClinicalTrials.gov (NCT03271242).