Developing a disease-specific quality of life measure for people with multiple sclerosis.

Abstract

To develop a patient-completed disease-specific measure of quality of life in multiple sclerosis and to validate the measure in a community-based population of people with multiple sclerosis. The items in the scale were selected in focus group sessions of people with multiple sclerosis. The initial scale included 25 items and was tested in subgroups of 150 people from a population register of people with multiple sclerosis in Leeds. Following further developmental phases, a restructured 16-item scale was tested on a random sample of 200 people with multiple sclerosis from the population register, stratified according to disease course. This led to a final eight-item unidimensional scale, the Leeds Multiple Sclerosis Quality of Life (LMSQoL) scale. After initial development a 16-item scale was found to be both reliable and valid. Cronbach's alpha for the 16-item scale was 0.86. The test-retest correlation was 0.74, using a two-week retest interval. However, convergent validity with the General Well Being Index was 0.67 and with the SF-36 Physical Function Scale was 0.68. This suggested that the scale straddled these two concepts and was confirmed by fit of the data to the Rasch measurement model. This revealed the potential for a reduced eight-item version of the scale. The eight-item scale had a closer association to well-being (0.83) than to physical function (0.39), had good internal consistency (0.79) and test-retest reliability (0.85). There were virtually no floor or ceiling effects for the scale. The study presents a disease-specific measure of quality of life in multiple sclerosis, the Leeds Multiple Sclerosis Quality of Life (LMSQoL) scale. The instrument is brief, easy to use and practical to administer in clinic or as a postal questionnaire. It measures a construct related to well-being, and provides an important adjunct to the measurement of outcome in multiple sclerosis.