Cross-cultural validity of four quality of life scales in persons with spinal cord injury

Background: Quality of life (QoL) in persons with spinal cord
injury (SCI) has been found to differ across countries. However,
comparability of measurement results between countries depends on
the cross-cultural validity of the applied instruments. The study
examined the metric quality and cross-cultural validity of the
Satisfaction with Life Scale (SWLS), the Life Satisfaction
Questionnaire (LISAT-9), the Personal Well-Being Index (PWI) and
the 5-item World Health Organization Quality of Life Assessment
(WHOQoL-5) across six countries in a sample of persons with spinal
cord injury (SCI). Methods: A cross-sectional multi-centre study
was conducted and the data of 243 out-patients with SCI from study
centers in Australia, Brazil, Canada, Israel, South Africa, and the
United States were analyzed using Raschbased methods. Results: The
analyses showed high reliability for all 4 instruments (person
reliability index .78-.92). Unidimensionality of measurement was
supported for the WHOQoL-5 (Chi(2) = 16.43, df = 10, p =.088),
partially supported for the PWI (Chi(2) = 15.62, df = 16, p =
.480), but rejected for the LISAT-9 (Chi(2) = 50.60, df = 18, p =
.000) and the SWLS (Chi2 = 78.54, df = 10, p =.000) based on
overall and item-wise Chi(2) tests, principal components analyses
and independent t-tests. The response scales showed the expected
ordering for the WHOQoL-5 and the PWI, but not for the other two
instruments. Using differential item functioning (DIF) analyses
potential cross-country bias was found in two items of the SWLS and
the WHOQoL-5, three items of the LISAT-9 and four items of the PWI.
However, applying Rasch-based statistical methods, especially
subtest analyses, it was possible to identify optimal strategies to
enhance the metric properties and the cross-country equivalence of
the instruments post-hoc. Following the post-hoc procedures the
WHOQOL-5 and the PWI worked in a consistent and expected way in all
countries. Conclusions: QoL assessment using the summary scores of
the WHOQOL-5 and the PWI appeared cross-culturally valid in persons
with SCI. In contrast, summary scores of the LISAT-9 and the SWLS
have to be interpreted with caution. The findings of the current
study can be especially helpful to select instruments for
international research projects in SCI.