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Reliability of manual wheelchairs: a repairable systems analysis
Anand Mhatre1, Muyun Zhao1, Colin Mair2
1Division of Occupational Therapy, School of Health and Rehabilitation Sciences, The Ohio State University College of Medicine, Columbus, Ohio, USA.
Purpose:
The study aims to develop and assess new reliability performance measures for lightweight (LW) and ultralightweight (UL) wheelchair devices using reliability engineering methods and compare them across wheelchair models.
Methods:
Wheelchair repair data from n = 969 manual wheelchairs prescribed by the National Health Service (NHS) between January 2007 and August 2014 in Greater Glasgow, Scotland, UK was analysed. Repairable systems analysis methods generated reliability performance measures, including Mean Cumulative Number of Failures (MCF), Repair Trend, Mean Time Between Failures (MTBF), and a Wheelchair Reliability Index (WRI). WRI is the MTBF divided by the average cost in pounds.
Results:
Four wheelchair models were analysed: two lightweight (LW1, n = 338; LW2, n = 328) and two ultralight (UL1, n = 120; UL2, n = 183) seating models. About 37% of LW units failed compared to 71% of UL ones. Models LW1, UL1, and UL2 demonstrated a linear repair trend, whereas LW2 exhibited an exponential one, with the UL models experiencing frequent failures, i.e. a higher mean cumulative number of failures than the lightweight models. After 2-3 years of use, the MCFs differed significantly between these models, p<.05. The MTBF ranged from 7 to 11 months over five years. Age negatively correlated with failure measures for LW2. WRI of UL models is 1/4th to 2/3rd compared to LW models. The MTBF values indicate variable check-up intervals for the models. The WRI indicators indicate that ultralight chairs have lower reliability in terms of the pound value.
Conclusion:
Our study findings highlight the urgent need for reliability performance monitoring and improvements in wheelchair follow-up.
