Development of the Instrumental Activities of Daily Living Scale-Ability and Actual Performance: A New Measure for People With Schizophrenia

Abstract

Objective The study was to develop the instrumental activities of daily living scale-ability and actual performance (IADL-AA) to assess the ability and actual performance constructs of instrumental activities of daily living (IADL).Methods Eight experts reviewed the items of the IADL-AA. Additionally, 30 and 266 people with schizophrenia participated in cognitive interviews and validation analysis, respectively. Expert consultations and cognitive interviews were conducted to examine face validity and content validity, respectively. Construct validity was evaluated through Rasch analysis to ensure unidimensionality. Convergent validity was investigated using Pearson’s r, discriminative validity was examined through floor and ceiling effects, and internal consistency was assessed using Cronbach’s alpha (α).Results The IADL-AA comprised 23 items showing the unidimensionality of each domain. The infit and outfit mean squares were 0.76–1.21 and 0.68–1.40, respectively. A moderate correlation was observed between ability and actual performance domains (r=0.63). No floor or ceiling effects were found for the two domains (0.0%–6.0% and 1.5%–3.0%, respectively). Cronbach’s α of the two domains was 0.83–0.90.Conclusion The IADL-AA demonstrates satisfactory psychometric properties, including face validity, content validity, construct validity, convergent validity, discriminative validity, and internal consistency. This measure can effectively identify the capacity and degree of independence of IADL function in people with schizophrenia.