title: Product limit estimation for capturing of pressure distribution dynamics.
abstract: Measurement of contact pressures at the wheelchair-seating interface is a critically important approach for laboratory research and clinical application in monitoring risk for pressure ulceration. As yet, measures obtained from pressure mapping are static in nature: there is no accounting for changes in pressure distribution over time, despite the well-known interaction between time and pressure in risk estimation. Here, we introduce the first dynamic analysis for distribution of pressure data, based on the Kaplan-Meier (KM) Product Limit Estimator (PLE) a ubiquitous tool encountered in clinical trials and survival analysis. In this approach, the pressure array-over-time data set is sub-sampled two frames at a time (random pairing), and their similarity of pressure distribution is quantified via a correlation coefficient. A large number (here: 100) of these frame pairs is then sorted into descending order of correlation value, and visualized as a KM curve; we build confidence limits via a bootstrap computed over 1000 replications. PLEs and the KM have robust statistical support and extensive development: the opportunities for extended application are substantial. We propose that the KM-PLE in particular, and dynamic analysis in general, may provide key leverage on future development of seating technology, and valuable new insight into extant datasets.
authors.affiliation: University of Hartford, Department of Rehabilitation Sciences, West Hartford, CT 06117, United States; Veterans Affairs Cooperative Studies Program, VA Connecticut Healthcare System, West Haven, CT 06150, United States; Yale School of Public Health, Department of Biostatistics, New Haven, CT 06520, United States.
authors.forename: Michael
authors.initials: M
authors.lastname: Wininger
authors.affiliation: University of Hartford, Department of Rehabilitation Sciences, West Hartford, CT 06117, United States. Electronic address: bcrane@hartford.edu.
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Crane
mesh_terms: D011312:Pressure; D013223:Statistics as Topic / Q000379:methods*
keywords: Correlation; Kaplan–Meier; Pressure; Product Limit Estimator; Time series; Ulcer; Wheelchair