Item distribution, scalability and internal consistency of the QUALIDEM quality of life assessment for patients with dementia in acute hospital settings

Background Quality of life (QoL) of people with dementia (PwD) is an important indicator of quality of care. Studying the impact of acute hospital settings on PwD's QoL requires assessment instruments that consider environmental factors. Until now, dementia-specific QoL instruments have not yet demonstrated their feasibility in acute hospitals because their use takes up too much time or their validity depends on observation periods that usually exceed the average length of hospital stays. Therefore, validated instruments to study QoL- outcomes of patients with dementia in hospitals are needed. Methods Data stem from a study that analyzed the impact of a special care concept on the QoL of patients with dementia in acute hospitals. Total sample size consisted of N = 526 patients. Study nurses were trained in using an assessment questionnaire and conducted the data collection from June 2016 to July 2017. QoL was assessed with the QUALIDEM. This instrument consists of nine subscales that can be applied to people with mild to severe dementia (N = 344), while six of the nine subscales are applicable for people with very severe dementia (N = 182). Scalability and internal consistency were tested with Mokken scale analysis. Results For people with mild to severe dementia, seven out of nine subscales were scalable (0.31 <= H <= 0.75). Five of these seven subscales were also internally consistent (rho >= 0.69), while two had insufficient reliability scores (rho = 0.53 and 0.52). The remaining two (positive self-image, feeling at home) subscales had rather low scalability (H = 0.17/0.16) and reliability scores (rho = 0.35/0.36). For people with very severe dementia, all six subscales were scalable (0.34 <= H <= 0.71). Five out of six showed acceptable internal consistency (rho= 0.65-0.91). Only the item social relations had insufficient reliability (rho = 0.55). Conclusions In comparison with a previous evaluation of the QUALIDEM in a long-term care setting, the application in a hospital setting leads to very similar, acceptable results for people with mild to severe dementia. For people with very severe dementia, the QUALIDEM seems to fit even better in a hospital context. Results suggest either a revision of unsatisfactory items or a general reduction to six items for the QUALIDEM, for all PwD. In general, the QUALIDEM can be recommended as instrument to assess the QoL for PwD in the context of hospital research. Additionally, an investigation of the inter-rater reliability is necessary because the qualification of the nurses and the length of stay