The Subjective Index for Physical and Social Outcome (SIPSO) in Stroke: investigation of its subscale structure

BACKGROUND Short and valid measures of the impact of a stroke on integration are required in health and social settings. The Subjective Index of Physical and Social Outcome (SIPSO) is one such measure. However, there are questions whether scores can be summed into a total score or whether subscale scores should be calculated. This paper aims to provide clarity on the internal construct validity of the subscales and the total scale. METHODS SIPSO data were collected as part of two parallel surveys of the met and unmet needs of 445 younger people (aged 18-65) with non-recent stroke (at least one year) and living at home. Factor, Mokken and Rasch analysis were used. RESULTS Factor analysis supported a two factor structure (explaining 68% of the variance) as did the Mokken analysis (overall Loevinger coefficient 0.77 for the Physical Integration subscale; 0.51 for the Social Integration subscale). Both subscales fitted the Rasch model (P > 0.01) after adjusting for some observed differential item functioning. The 10-items together did not fit the Rasch model. CONCLUSIONS The SIPSO subscales are valid for use with stroke patients of working age but the total SIPSO is not. The conversion table can be used by clinicians and researchers to convert ordinal data to interval level prior to mathematical operations and other parametric procedures. Further work is required to explore the occurrence of bias by gender for some of the items.