A short measure of balance in multiple sclerosis: validation through Rasch analysis

Ambulatory patients with multiple sclerosis (MS) frequently present with poor balance. Neither static nor dynamic posturography explore balance during self-paced movements in real-life activities, when fall is most probable. Behavioural item-response scales can easily represent these activities. However, testing many items can easily cause fatigue in MS patients, thus distorting their scores. On the other hand, the lower the number of items, the lower the precision of the cumulative score and its reliability. A new short instrument was derived from existing ones (the Tinetti and the Berg balance scales). A preliminary 10-item version encompassed sit/stand manoeuvres, standing with eyes open and closed, standing with eyes closed and head extended, leaning forward while standing, picking up an object from floor, resisting nudges on the sternum, turning around, tandem stance. The instrument was administered 1-3 times to 55 MS patients (103 observations overall), all of them able to walk autonomously for at least 20 metres. The Rasch Analysis was adopted to explore the psychometric validity of the scale. Two items (Stand-to-sit and Standing with eyes open) were deleted, as they were too easy and thus uninformative. The remaining 8 items made up a scale (called EQUI-SCALE) complying with the requirements of unidimensionality and reliability. The item scores remained stable in a sub-sample of 24 patients tested before and after ten 1-hour exercise sessions, thus supporting the homogeneity of the items.