Internal consistency and structural validity of the Swiss easy-read Integrated Palliative Care Outcome Scale for People with dementia: a secondary exploratory factor analysis.

Abstract

Background: The Integrated Palliative Care Outcome Scale for People with Dementia (IPOS-Dem) was developed as a promising person-centred proxy measure of symptoms and concerns. We used the Swiss-German easy-read version, a measure designed to be completed individually by family members and frontline staff caring for people with dementia. In this secondary data analysis of multicentre trial data, we investigate the IPOS-Dem's structural validity and internal consistency of the version.

Methods: A total of 257 people with dementia were assessed by frontline staff, while family members assessed 118 people residing in one of 23 participating Swiss-German long-term care facilities. Each IPOS-Dem version, corresponding to the two rater populations (family members and frontline staff), underwent exploratory factor analysis separately, using data from one assessment per person with dementia. A minimum residual solution with varimax rotation was calculated to determine the factor structure. Item reduction decisions were based on factor loadings and indices for internal consistency.

Results: The construct validity of the Swiss-German easy-read IPOS-Dem for frontline staff is demonstrated by two factors: Dementia Interaction and Physical Impact (Cronbach's α = 0.83) and Dementia Emotional and Behavioural Impact (Cronbach's α = 0.81). Four factors, with Cronbach's α ranging from 0.77 to 0.86, were computed for the family member version: Dementia Interaction Impact, Easy-to-Assess Dementia Physical Impact, Hard-to-Assess Dementia Physical Impact and Dementia Emotional and Behavioural Impact.

Conclusions: Like other reduced patient-related outcome measures, palliative care measures and their parent instrument IPOS we identified subscales in the easy-read IPOS-Dem that describe a psychosocial impact and a physical impact. Differences in the internal structure of the family and staff versions of the IPOS-Dem likely stem from variations in observation intervals, roles and perspectives, with family members often focusing on loss and past experiences whereas staff may equate quality of life with quality of care leading to differing ratings. However, the identified internal consistency indices between 0.77 and 0.86 indicate acceptable internal consistency for the subscales and the IPOS-Dem should be taken forward for further psychometric evaluation.

Trial registration: The overarching trial has been approved by the Swiss Regional Ethics Committee of the Canton of Zürich as the leading ethics committee for the involved regions, with clearance certification number BASEC2019-01847 (12/11/2019). The main study and secondary analysis are registered with the German Clinical Trials Register (DRKS00022339, 05/10/2020). Full registration is available online at http://www.drks.de/DRKS00022339 .