Confirmation and extension of the validity of the Multiple Sclerosis Walking Scale-12 (MSWS-12)
Introduction
Walking ability is often used by researchers and clinicians as a measure of disease progression in individuals with MS. There are multiple measures of walking that have been included in clinical trials and practice, such as Timed Walk Tests (e.g., 25-ft or 6-min walk tests), quantitative movement analysis (i.e., gait kinematics), Ambulation Index, and the Expanded Disability Status Scale (EDSS) [1]. Importantly, all of those measures have limitations as assessments of walking ability, [1] thereby serving as the impetus for developing the Multiple Sclerosis Walking Scale-12 (MSWS-12) [2]. The MSWS-12 is a 12-item patient-rated measure of the impact of MS on walking that was developed using standard methods of test construction and then validated in community and hospital-residing samples of individuals with MS [2]. The initial evidence for the validity of MSWS-12 scores was subsequently confirmed in community-residing and hospital outpatient samples of individuals with MS [3]. As validation of scores from a measure is an ongoing and evolving process, [4], [5] the provision of additional evidence is warranted that further establishes the validity of inferences from scores on the MSWS-12. Therefore, we conducted analyses that both confirmed and extended the validity of inferences from the MSWS-12 in a community-based sample of individuals with MS. We initially tested the factorial or structural validity of a uni-dimensional model for MSWS-12 scores and then confirmed the previously reported pattern of correlations between scores from MSWS-12 with the EDSS and subscales of the Multiple Sclerosis Impact Scale (MSIS-29) [6]. We then extended previous research by first examining the correlation between scores from the MSWS-12 with an objective measure of walking provided by accelerometry and second examining the pattern of correlations between MSWS-12 scores with walking and non-walking related subscales of the Multiple Sclerosis Related Symptom Checklist (MS-RS) [7] and Performance Scales (PS) [8].
Section snippets
Participants
Participants (N = 133) were recruited through support group meetings of the Greater Illinois and Indiana State Chapters of the National Multiple Sclerosis Society. The mean age of the sample was 51.1 years (SD = 11.1) and the sample was primarily female (n = 104, 78%), Caucasian (n = 123, 93%), employed (n = 71, 53%), married (n = 91, 68%) and well educated (some college education n = 36, 27%; college graduate n = 61, 46%). The mean duration of time since MS diagnosis was 12.0 years (SD = 9.0). The sample
Descriptive statistics
Mean scores, standard deviations, and ranges of scores for the measures included in the study are presented in Table 1.
Factorial validity
The single-factor model provided an adequate fit for MSWS-12 scores (χ2 = 88.71, df = 18, p < .001, SRMR = 0.04, CFI = 0.99) and all factor loadings were statistically significant (p < .001) and strong in magnitude (mean factor loading = .92, range = .84–.97).
Internal consistency
The internal consistency of scores from the MSWS-12 was acceptable (α = .97).
Bivariate correlation analysis: confirming previous validity evidence
The correlations between MSWS-12 scores and scores from the
Discussion
Validation of scores from a measure is an ongoing and evolving process [5]. Therefore, we conducted analyses that both confirmed and extended the validity of inferences from MSWS-12 scores in a community-based sample of individuals with MS. The confirmatory factor analysis provided novel evidence that a uni-dimensional or single-factor model provided an adequate fit for MSWS-12 scores. This indicates that scores from MSWS-12 items can be summed into a composite or overall measure of walking
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