Psychometric Properties of the "Modified Postural Assessment Scale for Stroke Patients"
Date Issued
2008
Date
2008
Author(s)
Huang, Wen-Shing
Abstract
Background and purposes: In this study, four balance testing items of moderate-high difficulty level were added to the original Postural Assessment Scale for Stroke Patients (PASS) to form the modified PASS (mPASS), in an attempt to reduce the ceiling effects and plateau phenomenon found in studies using the PASS to assess postural control ability in patients with stroke. The purposes of this study were to investigate the discriminant validity of the four new items (mPASS-4) and the mPASS, as well as the reliability, internal consistency, concurrent and predictive validity, and responsiveness of the mPASS. ethods: The study was divided into three parts. In Part I of the study, 63 patients with stroke (mean age= 61.5 yrs) participated and were divided into the mild (National Institutes of Health Stroke Scale (NIHSS) < 4), moderate (4≦NIHSS≦15), and severe (NIHSS>15) subgroups. All participants performed the mPASS on the 14th day post stroke onset (D14). The Mann-Whitney statistics was used to investigate the differences in mPASS-4, mPASS total, and PASS total scores among the three subgroups. The principal components analysis (PCA) was used to investigate the primary factors underlying the mPASS. In Part II of the study, 5 patients of each severity level of stroke were randomly selected from the 63 patients in Part 1. Seven independent raters evaluated the mPASS performance of these 15 patients recored on videotapes twice with a two-week interval. The ICCs(2,1) and weighted kappa analyses were used to investigate the intra- and inter-rater reliability for the total mPASS scores and item scores, respectively. The Cronbach alpha was analyzed to investigate the internal consistency of the mPASS. In Part III of the study, a cohort design was used and another 39 patients with stroke participated, among which 27 of them completed the longitudinal follow-up assessments of the mPASS, Berg Balance Scale (BBS), Trunk Control Test (TCT), Barthel Index (BI), modified Rankin Scale (mRS), and the Timed “Up and Go” Test (TUGT) on D14, D30, and D90. The Spearman correlation coefficients were used to analyze the concurrent validity (mPASS versus PASS, BBS, and TCT on D14, D30 and D90) and predictive validity (mPASS on D14 and D30 versus BBS, BI, mRS, and TUGT on D90). In addition, the receiver operating characteristics curve (ROC curve) analysis was used to investigate the sensitivity and specificity of using the mPASS score on D14 in predicting the mRS score on D90. esults: In Part I, the results showed that the mean score of the mPASS-4 (1.3-1.5) ranged inbetween that of the B12 (moderate difficulty level, mean= 1.8) and that of the A4 and A5 (high difficulty level, mean= 1.1 and 0.8, respectively). The mPASS-4 and total mPASS scores, but not the B12, A4, A5, and the total PASS scores, showed significant differences (p < 0.05) between patients with mild versus moderate severity of stroke. Results of the PCA revealed that the mPASS had two domains and the mPASS-4 belonged to the “balance control in standing without support” domain. Results of the Part II of the study showed excellent inter- and intra-rater reliability, and internal consistency of the mPASS. The ICCs of the total mPASS scores for intrarater reliability ranged between 0.9992 and 1, and those for interrater reliability ranged between 0.9992 and 0.9999. The weighted kappa of all mPASS item scores for intrarater reliability ranged from 0.833 to 1.000 and from 0.858 to 1.000 for interrater reliability. The Chronba alpha values among all mPASS items ranged from 0.9610 to 0.9625. Results of the Part III showed that the mPASS had good concurrent and predictive validity, and responsiveness. The total mPASS scores performed on D14, D30, and D90 were highly correlated with thoses of the PASS and BBS performed on the same testing dates (rs = 0.950~0.983, p < 0.05). The total mPASS scores performed on D14 and D30 were both moderately to highly correlated to the scores on BBS, TUGT, BI and mRS performed on D90 (rs = 0.835, -0.795, 0.767, and -0.843, respectively, for D14; rs = 0.889, -0.847, 0.748, and -0.820, respectively, for D30; all p < 0.05). In addition, results of the ROC analysis showed that a cutoff score set at 35 point on mPASS could significantly predict an mRS score of equal to or below 2 on D90 with the sensitivity being 81.2%, specificity being 90.9%, and the area under the ROC curve being 0.915. Regarding the responsiveness, the results showed that the effect sizes of the changes in mPASS scores from D14 to D30, D30 to D90, and D14 to D90 were 1.19, 0.76, and 1.22, respectively for all participants. The effect sizes of these changes for patients with different severity also were moderate (0.73) to large (>0.80). iscussion and Conclusions: The mPASS-4 and mPASS had good discriminant validity, and mPASS also had good psychometric properties, including high intrarater reliability, interrater reliability, internal consistency, concurrent validity, predictive validity and responsiveness. However, further studies are needed to determine whether the ceiling effect of mPASS on D90 would still exist if a greater portion of patients with severe stroke were recruited.
Subjects
postural control
psychometrics
stroke
reliability
validity
responsiveness
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