A dependency model for patients with Alzheimer's disease: its validation and relationship to the costs of care - the LASER-AD study

Background: Loss of independence becomes more marked as Alzheimer's disease (AD) progresses and contributes significantly to its societal and economic burden. Existing measures of functional disability focus either on basic or on instrumental activities of daily living (ADL). It would be more appropriate to combine these but, using existing assessment tools, this would involve considerable quantitative analysis. Recently, a qualitative and pragmatic system of classifying AD patients according to levels of dependency has been developed in a Belgian cohort. Objectives: To validate independently, in a UK community setting, a functional classification model of AD patients and to explore the relationship between dependency and costs of care using this model. Research design and methods: Longitudinal epidemiological study of 224 AD patients. Data were collected at baseline and at 6 months on ADL, global state, cognition, behavioural dimensions, depression, quality of life and resource utilisation using validated instruments. An automatic classification algorithm was performed to allow identification of dependency clusters. The scheme was tested for validity against other simultaneously collected data including health and social care costs. The relationship between dependency and costs of care was explored using ANOVA models. Results: Analysis of the ADL assessment instruments produced three ADL sub-scores by which patients could be classified into one of three disability clusters: ('non-dependent', 'non-dependent with instrumental functional disability', and 'dependent'). Good external validity of the classification scheme was demonstrated by correlation with simultaneously collected data. After a backward selection process on ANOVA model (at a 5% level), institutionalisation and the most dependent status were the most significant cost drivers. Conclusions: Qualitative classification of AD patients using dependency levels is a simple and validated approach. Applying this approach showed that institutionalisation and the most 'dependent' status were independently and significantly associated with high care cost.