Exploratory factor analysis of the Mini instrument for the observer rating according to ICF of Activities and Participation in Psychological disorders (Mini-ICF-APP) in patients with severe mental illness

Objectives After publication of the WHO International Classification of Functioning, Disability and Health (ICF), the Mini-ICF-APP (Mini instrument for the observer rating according to ICF of Activities and Participation in Psychological disorders) was derived and validated in three languages to assess limitations in activities or capacities and restrictions in participation in patients with mental illness. Although the Mini-ICF-APP has been demonstrated to have sound psychometric properties, factor analytic studies of this instrument have not been conducted, and the total score is generally used. We aimed at examining the structure of this instrument, in order to identify possible factors, which would allow a more sensitive measurement of an individual's specific limitations. Methods Patients with schizophrenia or bipolar disorder attending a community mental health center were recruited consecutively over an index period and underwent standardised assessment, including the 13-item Mini-ICF-APP 24-item and Personal and Social Performance scale and the Brief Psychiatric Rating Scale (BPRS-24). Factor analysis with maximum likelihood estimation and oblique rotation was performed on Mini-ICF-APP items. Results A three-factor solution provided the best goodness of fit indices. Factors were interpreted as proficiency, relational capacity and autonomy. Factor scores were significantly higher in patients with schizophrenia than in those with bipolar disorder. The 'proficiency' factor exhibited the strongest associations with BPRS, CGI-S and total PSP. Moreover, correlations between Mini-ICF-APP factors and PSP dimensions were in the expected direction, indicating good convergent and discriminant validity of the instrument; in fact, the highest correlations were found between the corresponding factors/dimensions of the two instruments (proficiency with PSP socially useful activities, relational capacity with PSP personal and social relationships, autonomy with PSP self-care) and the lowest correlations were observed with PSP dimension 'disturbing and aggressive behaviour, that is not assessed in the Mini-ICF-APP. Conclusions The factors extracted are clearly interpretable and have convergent/discriminant validity. Our findings may have clinical implications, as the distribution of factors distinguishes the two patient groups, which may require different interventions to achieve an optimal therapeutic response.