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Interpreting change scores on the Amyotrophic Lateral Sclerosis Assessment Questionnaire (ALSAQ-40)

V Peto

Health Services Research Unit, University of Oxford, Institute of Health Sciences, Oxford

G Jones

Institute of General Practice and Primary Care, University of Sheffield, Northern General Hospital, Sheffield

R Fitzpatrick

Department of Public Health, University of Oxford, Institute of Health Sciences, Oxford, UK

Objectives: To determine the amount of change over time on the five dimensions of the 40-item Amyotrophic Lateral Sclerosis Assessment Questionnaire (ALSAQ-40) that are subjectively meaningful to patients. Minimally important differences (MID), effect sizes (ES) and standardized response means (SRM) are calculated for respondents who indicate only a little change over the time of the study whilst mean change scores, ES and SRM statistics are calculated for those who indicated much change.

Design: Postal survey. Copies of the ALSAQ-40 were completed on two occasions three months apart. Respondents were also asked to indicate how much change they had experienced since baseline on each of the five domains of the questionnaire.

Setting: All patient members of the Motor Neurone Disease Association for England, Wales and Northern Ireland.

Subjects: Seven hundred and sixty-four patient members returned questionnaires at baseline and follow-up.

Results: For those reporting minor change since baseline results varied across dimensions. For example a MID was reflected in a change of 6.67 (SD 16.52) points for the Communication dimension, whilst for the Emotional functioning dimension the change was 2.67 (SD 15.45) points. Similarly ESs and SRMs varied considerably across dimensions. Mean change over time, ES and SRM statistics for those who reported that their health was much worse at follow-up were substantially larger: for example, mean changes ranged from 6.87 (SD 15.87) to 13.79 (SD 22.60).

Conclusions: Results indicate the minimum magnitude of change that is subjectively meaningful to patients. Results indicate that smaller changes than have been suggested previously as significant have a subjectively meaningful adverse effect upon patients.

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