The psychometric properties of ADCS - activities of daily living inventory and comparison of different ADL scores

Several multi-item activities of daily living (ADL) scales have been developed for assessment of functional status of patients with Alzheimer’s Disease (AD) in the last few decades. A disadvantage of the large number of scales is that scores of different ADL scales cannot be compared directly with each other. ADL scales which are used by McNamee’s (Townsend's disability scale) and Hill’s (Medicare Beneficiary definitions and Katz index of ADL) provide suitable tools for modelling the cost-effectiveness of different treatments in patients with Alzheimer’s disease, since they report empirical results about the relationship between the degree of functional impairment (healthcare costs) and the prevalence of institutionalisation. The IDEAL trial examines the efficacy of Exelon Patch with the ADCS - Activities of Daily Living Inventory (ADCS-ADL). This ADL instrument is not directly comparable to the ADL scales used by McNamee and Hill. However, the use of the ADL scale from the IDEAL study to predict the prevalence of institutionalisation with scales by Hill and McNamee would be desirable. Because of the generic nature of the ADL construct, and considering the fact that these well validated ADL instruments identify the main physical impairments and functional disabilities in Alzheimer's disease, we should expect high overlap in item content between different ADL instruments. The high overlap in item content between instruments, and the similar wording and scoring criteria, makes it possible to pair each impairment with another. The intention of this study was to establish the link between these ADL scales in order to provide appropriate conditions for further economic analyses on the dataset provided by the IDEAL study