The development of a scale of the Guttman type for the assessment of mobility disability in multiple sclerosis

Abstract

Objective: To develop a valid and reliable scale of the Guttman type for the assessment of mobility disability in multiple sclerosis (MS). Subjects: Sixty-eight subjects with a definite diagnosis of MS participated. They were living in the community and attending as outpatients at a MS unit at a District General Hospital. Thirty had the primary progressive pattern of disease, and 38 had the relapsing–remitting pattern. Methods: Formal assessments used for neurological disability were inspected, and 14 test items of gross motor function were extracted and ordered according to criteria. These were that tests required trunk control and did not require isolated movement at a single limb or body segment, that actions progressed from lying, to sitting, to standing and walking tasks, proceeding from broader to narrower bases of support. All subjects carried out all test items which were scored as ‘pass’ or ‘fail'. Analysis: Data were tested for internal consistency, reliability, inter-item correlation, reproducibility and scalability. On the basis of the results, the items were reordered in rank, and reduced to 11 tests. The 11-item scale was reanalysed. Results: Results showed that the scale had an internal consistency of 0.88 (α coefficient) and a coefficient of reproducibility (CR) of 0.95 and above for both MS subject groups. The coefficient of scalability (CS) for items was 0.78 for primary progressive subjects and 0.74 for the relapsing–remitting group. Reliability ranged from moderate (kappa = 0.49) for one item, to perfect for six items. Conclusion: The scale was demonstrated to be a hierarchical scale of the Guttman type exhibiting homogeneity and good reliability. The high CR indicated that scores may be summed, and the very acceptable levels of CS indicated that the cumulative scores are meaningful within the defined concept of hierarchy used in this study.