Kinematic Validation of a Multi-Kinect v2 Instrumented 10-Meter Walkway for Quantitative Gait Assessments
Authors: Bert H Coolen
Daphne J Geerse
Melvyn Roerdink
Journal: PLoS ONE (2015)
Discipline: Multidisciplinary
Keywords: Walking ability; 10-meter walking test (10MWT); Kinect v2 sensors; quantitative gait information; body point's time series
Affiliations: MOVE Research Institute Amsterdam, Department of Human Movement Sciences, VU University Amsterdam, Amsterdam, The Netherlands; Department of Neurology, Leiden University Medical Center, Leiden, The Netherlands., MOVE Research Institute Amsterdam, Department of Human Movement Sciences, VU University Amsterdam, Amsterdam, The Netherlands.

Abstract:  Walking ability is frequently assessed with the 10-meter walking test (10MWT), which may be instrumented with multiple Kinect v2 sensors to complement the typical stopwatch-based time to walk 10 meters with quantitative gait information derived from Kinect's 3D body point's time series. The current study aimed to evaluate a multi-Kinect v2 set-up for quantitative gait assessments during the 10MWT against a gold-standard motion-registration system by determining between-systems agreement for body point's time series, spatiotemporal gait parameters and the time to walk 10 meters. To this end, the 10MWT was conducted at comfortable and maximum walking speed, while 3D full-body kinematics was concurrently recorded with the multi-Kinect v2 set-up and the Optotrak motion-registration system (i.e., the gold standard). Between-systems agreement for body point's time series was assessed with the intraclass correlation coefficient (ICC). Between-systems agreement was similarly determined for the gait parameters' walking speed, cadence, step length, stride length, step width, step time, stride time (all obtained for the intermediate 6 meters) and the time to walk 10 meters, complemented by Bland-Altman's bias and limits of agreement. Body point's time series agreed well between the motion-registration systems, particularly so for body points in motion. For both comfortable and maximum walking speeds, the between-systems agreement for the time to walk 10 meters and all gait parameters except step width was high (ICC ≥ 0.888), with negligible biases and narrow limits of agreement. Hence, body point's time series and gait parameters obtained with a multi-Kinect v2 set-up match well with those derived with a gold standard in 3D measurement accuracy. Future studies are recommended to test the clinical utility of the multi-Kinect v2 set-up to automate 10MWT assessments, thereby complementing the time to walk 10 meters with reliable spatiotemporal gait parameters obtained objectively in a quick, unobtrusive and patient-friendly manner. 

Retracted: No

PubPeer comments:
 In this paper, the author defined a compatibility index of two interval valued matrices in Definition 2.6 as a normalized $L_1$ vector distance. It is technically ok as a distance measure between two interval valued matrices but is **flawed** as a **compatibility index** in this context for **measuring the consensus among the decision makers.** Note that for a pairwise comparison matrix, the diagonal elements are always fixed, which means that there would be no deviation for the diagonal elements when measuring the consensus between two pairwise comparison matrices. As a result, Definition 2.6 systematically **underestimates the compatibility** of two such matrices. It should be calibrated to remove the bias. ![file] ![file] ![file] , 
 Dear Rhipidura Albiventris, Thank you for your interest in our work and for sharing your concerns. The corresponding replies are as follows: In group decision making process, the consensus among the decision-makers can be reached by multiple ways under diverse environments, for example: (1) Calculating the total amount of opinion changes for all decision-makers, which is similar to the minimum cost consensus problems; (2) According to the Analytic Hierarchy Process (AHP) and consistency reaching process, AHP-based consensus models are used to achieve consensus, etc. This paper belongs to the first method and calculates the average of total deviations for all decision-makers, and then presents the compatibility index. The index is reasonable as you said. There is no deviation for the diagonal elements of two pairwise comparison matrices. I agree with you on this. For example, in the preference relation matrices, the diagonal elements are 1 if we use the Saatyu2019s 1-9 ratio; the diagonal elements are S_0 if we use the symmetry linguistic term sets, etc. Through the calculation process, the compatibility results are not affected by diagonal elements. Thus, Definition 2.6 is reasonable. We feel sorry that it has not clearly stated in Definition 2.6. However, in future research, one may improve our research contents, such as only taking the upper triangular elements in the symmetric matrix into account. Best regards ,