Development and factor analysis of an index of post-polio sequelae

PURPOSE: This present study describes the development, factor structure and initial validation of the Index of Post-Polio Sequelae (IPPS). METHOD: The IPPS was tested on a sample of 849 community-dwelling polio survivors between the ages of 40 and 93 years old who participated in a large, national study of menopause and aging in late polio. Items from the IPPS were submitted to a factor analysis using principal components extraction and rotated to oblique simple structure using promax rotation. Convergent validity was assessed using bivariate correlation. RESULTS: Three factors were extracted that accounted for approximately 53% of the variance in the original IPPS items. Factor 1 (Pain) was loaded most heavily by two items referring to muscle and joint pain. Factor 2 (Atrophy) was loaded by items referring to muscle atrophy, involved muscle weakness, and fatigue. Factor 3 (Bulbar) was comprised of two items referring to breathing and swallowing problems. Bivariate correlations between health and psychosocial variables and each of the factors all were significant and in expected directions. CONCLUSIONS: This first validation of a standardized scale to assess the severity of post-polio sequelae in polio survivors suggests a psychometrically sound instrument whose factor structure represents commonly reported problems in the extant post-polio literature.