Validity and reliability of the video-based standing-start 180° turn test (SS-180) in adults with and without Parkinson's disease (PD)

Stack, E., Ashburn, A. and Rassoulian, H. (2002) Validity and reliability of the video-based standing-start 180° turn test (SS-180) in adults with and without Parkinson's disease (PD). Movement Disorders, 17 (S5), S116 -S165. (doi:10.1002/mds.10351).

Abstract

Objectives: To establish the external validity, test–retest characteristics and intra- and inter-rater reliability of the video-based SS-180.
Background: The SS-180 is being developed to facilitate research on dysfunctional turning, a common problem in PD; quick and easy to administer, it was designed for use beyond the laboratory setting. Subjects walk twice to a target 3 m behind them, first turning 180° in an unspecified direction, then requested to turn the opposite way. Turning Steps and Time (Section 1), Turn Type (Section 2) and Independence, Continuity, Ground Clearance, Stability and Posture (Section 3, scored 0–5) are then rated from video.
Methods: Thirty-eight adults with and without PD completed the SS-180 in a gait laboratory. To externally validate Sections 1 and 2, the video rating of 20 turns was compared with 3D motion analysis. Test–retest characteristics were established by testing 7 participants twice. Ten turns were rated twice by the lead researcher (with a week’s interval) to establish intra-rater reliability and by two researchers to establish inter-rater reliability.
Results: Agreement between video- and motion-analysis was moderate for Step Count (weighted 0.57) and good for Turn Type ( 0.78,95% CI 0.70 to 0.86). The mean difference between Times rated both ways was 0.02 sec in controls (95% limit of agreement 0.46 sec to 0.5 sec) and 0.9 sec in PD (95% limit of agreement 20% to 7%, logarithmically transformed). When retested, controls turned as before but a median 0.2 secfaster. In PD, Step Count was a median one less and the turn a median 0.6sec faster when repeated; Turn Type did not change and the Section 3 Score never changed more than one point, with the median change zero. The lead researcher’s two ratings were in 100% agreement for Step Count, Turn Type and Section 3 Score; mean Time difference was 0.13 sec (95% limit of agreement 0.37 sec to 0.11 sec). Between raters, agreement was good for Step Count ( 0.70), very good for Section 3 Score ( 0.82) and 100% for Turn Type; mean Time difference was 0.03 sec (95% limit of agreement 0.42s to 0.48 sec).
Conclusions: Video-rating the SS-180 produced results comparable with a laboratory-based gold standard; turns changed minimally when repeated and reliability proved acceptable, so research findings can be interpreted with confidence. The SS-180 is in use and being refined for clinical application.

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