Whose quality of life is it anyway? The validity and reliability of the Quality of Life-Alzheimer's Disease (QoL-AD) scale

Abstract

Quality of life (QoL) is becoming an increasingly used outcome measure in both clinical practice and research. There are now more than 1000 scales available to measure QoL, and it is important that they are assessed for reliability and validity. This study aims to assess the reliability and validity of the Quality of Life-Alzheimer's Disease (QoL-AD) scale, which is dementia specific and brief and uses the patient's own responses. Two separate samples of people with dementia (sample 1, n = 60; sample 2, n = 201) were assessed. Five focus groups were conducted involving both people with dementia and their caregivers; the focus groups showed that people with dementia had higher hopes for their QoL than their caregivers did for them. Questionnaires about the scale were completed by 71 health care professionals working with people with dementia. The scale was found to have good content validity with no additional items required and all items necessary. It also correlated well with the Dementia Quality of Life scale (0.69) and with the Euroqol-5D scale (0.54), indicating good criterion concurrent validity. Construct validity was also good with the principal components analysis showing all 13 items of the QoL-AD loaded on component 1. Interrater reliability was excellent with all Cohen's kappa values >0.70. Internal consistency was excellent with a Cronbach's alpha coefficient of 0.82. Some people with severe dementia and a Mini-Mental State Examination score as low as 3 were able to satisfactorily complete the QoL-AD. The QoL-AD has very good psychometric properties and can be completed with people with a wide range of severity of dementia.