Health-related quality of life in amyotrophic lateral sclerosis: determining a meaningful deterioration.

This paper uses the standard error of measurement (SEM) and the standard error of the difference (S(diff)) in relation to data on individuals with amyotrophic lateral sclerosis (ALS) to calculate the minimum change scores required by statistical criteria for each dimension of the Amyotrophic Lateral Sclerosis Assessment Questionnaire (ALSAQ-40). Data collected from a longitudinal study was used to evaluate the usefulness of SEM and S(diff) criteria and to compare these criteria with an anchor-based approach in determining meaningful change. Questionnaires were completed on two occasions, 3 months apart. 764 questionnaires were returned. Questionnaires included the ALSAQ-40 and dimension specific transition items. The ALSAQ-40 is a disease specific health-related quality of life instrument for use in studies of patients with ALS or other motor neuron diseases. For all dimensions of the ALSAQ-40 the patterns of SEMs were similar over time. The results suggest that, for example, six points change on a 0-100 transformed scoring of the physical mobility dimension may be considered on distributional grounds a minimum meaningful change. The demonstrated consistency of SEMs for the dimensions of the ALSAQ-40 is empirical evidence of the theoretically claimed advantage of this measure of sample independence, and supports use of this distributional approach to calculate meaningful change.