Health Technol Assess. 2004 Mar;8(9):1-60
Hobart JC, Riazi A, Lamping DL, Fitzpatrick R, Thompson AJ.
Neurological Outcome Measures Unit, Institute of Neurology, London,
UK.
OBJECTIVES:
To develop a patient-based, disease-specific measure of the health impact of multiple sclerosis (MS) for use in clinical trials and clinical practice.
DATA SOURCES:
People with MS.
Members of the MS Society of Great Britain and Northern Ireland.
METHODS:
Standard psychometric methods were used to develop the Multiple Sclerosis Impact Scale (MSIS-29) in three stages.
Stage 1 (item generation): questionnaire items were generated from 30 patient interviews on the impact of MS on their lives, expert opinion and literature review.
Stage 2 (item reduction and scale generation): the questionnaire developed in stage 1 was administered by postal survey to 1530 randomly selected members of the MS Society.
Standard item reduction techniques were used to develop a rating scale from the pool of questionnaire items.
Stage 3 (psychometric evaluation): the questionnaire was evaluated for data quality, scaling assumptions, acceptability, reliability and validity in a separate postal survey of 1250 MS Society members.
Responsiveness was evaluated in 55 people admitted to hospital for rehabilitation and intravenous steroid treatment of MS relapses.
RESULTS:
Stage 1 resulted in a 129-item questionnaire.
Stage 2 resulted in a 29-item rating scale measuring the physical and psychological impact of MS.
The MSIS-29 satisfied all recommended psychometric criteria for rigorous measurement.
Data quality was excellent: missing data were low, item test-retest reliability was high and scale scores could be generated for over 98% of respondents.
Item descriptive statistics, item convergent and discriminant validity, and factor analysis supported summing items to produce two summary scores.
MSIS-29 physical and psychological scale scores showed good variability, low floor and ceiling effects, good internal consistency and test-retest reliability.
Correlations with other measures and confirmation of hypotheses about group differences provided evidence for the validity of the MSIS-29 as a measure of the physical and psychological impact of multiple sclerosis.
Effect sizes provided preliminary evidence for responsiveness.
CONCLUSIONS:
The 29-item MSIS-29 is a rigorous new measure of the physical and psychological impact of MS.
All psychometric criteria were satisfied and there is preliminary evidence of responsiveness.
The MSIS-29 is particularly appropriate for use in clinical trials to evaluate therapeutic effectiveness from the patient's perspective.
Further critical evaluations of the MSIS-29 completed by people with neurologist-confirmed MS in different settings are suggested.
Head-to-head comparisons of the psychometric properties of the MSIS-29 and other outcome measures for MS will help to determine the relative advantages of different instruments so that the choice of measures for studies can be evidence based.