Measuring quality of life of persons with spinal cord injury: substantive and structural validation

The purpose of this study was to evaluate the substantive and structural validity of an existing measure of quality of life (QOL), the spinal cord injury (SCI) version of the Ferrans and Powers quality of life index (QLI). To evaluate substantive validity, 11 individuals with a SCI participated in 'think aloud' interviews to determine meaningfulness of the QLI items and to identify areas requiring modification. Free sort and ranking exercises of the items were used to evaluate the structural validity of the domains and scoring rubric. Content analysis of the interview comments resulted in the addition of two items and wording revision to three items. The free sort exercise revealed that the domains as perceived by the participants differed somewhat from those of the test developer. The contribution of the satisfaction and importance sections proposed by the scoring model was not completely supported by the data from the ranking exercise. It is concluded that the modified version of the QLI reflects the perspectives of persons with SCI spinal cord injury as represented by the participants of this study. The structural validity evaluation has implications for the use of domain subscores and weighted vs. section scores. Further evaluation of the modified version is necessary before widespread use with this patient population.