Confirmatory Factor Analysis of the Quality of Life in Alzheimer's Disease Scale in Patients with Alzheimer's Disease

Background/Study Context: Quality of life (QoL) has become an important outcome measure in clinical trials for Alzheimer's disease (AD). The Quality of Life in Alzheimer's Disease (QoL-AD) Scale is widely used for assessing QoL of patients with AD. This research aims to determine the factor structure of the QoL-AD Scale in AD patients. Methods: One hundred thirty-nine patients with mild-to-moderate AD were administered the QoL-AD Scale. Based on the model proposed for healthy people, confirmatory factor models were built using modification indices and residual analysis to improve the model fit. Results: Confirmatory factor analysis indicated poor fit for both the initial model and the single-factor model. Two models showed a good fit: a three-factor model (perceived health, perceived environment and perceived functional ability) and a two-factor model (perceived physical health and perceived psychological health). Because no differences in fit were found between both models, the authors proposed the more parsimonious solution as the best model. Conclusion: These results provide evidence supporting the construct validity of the QoL-AD Scale. This instrument seems to measure the perception of two related constructs (behavioral competence and environment) and could be used together with instruments measuring psychological well-being and the perception of health.