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Abstract
Companies routinely perform life tests on their products. Each of these life tests typically involves testing several units simultaneously with interest in the times to failure. Two aspects often associated with lifetime data that make the development of a control-charting procedure more demanding are that the data tend to be nonnormally distributed and censored. In this paper, one-sided lower and upper likelihood-ratio—based cumulative sum (CUSUM) control charting procedures are developed for Type I right-censored Weibull lifetime data to monitor changes in the scale parameter, also known as the characteristic life, for a fixed value of the Weibull shape parameter. Because a decrease in the characteristic life indicates a decrease in the mean lifetime of a product, a one-sided lower CUSUM chart is the main focus. We illustrate the development and implementation of the chart and evaluate its properties through a simulation study. The proposed CUSUM chart is compared with an exponentially weighted moving-average (EWMA) chart using the steady-state average run length (ARL) performance. The CUSUM chart is shown to perform better than the EWMA chart in detecting shifts for which it is designed.
Additional information
Notes on contributors
Rebecca M. Dickinson
Ms. Dickinson is a PhD Candidate in the Department of Statistics. Her email address is [email protected].
Denisa A. Olteanu Roberts
Dr. Olteanu Roberts is Co-Founder and Consultant at Olteanu & Roberts Analytics and Adjunct Faculty in the Department of Statistics member in the Department of Statistics at Virginia Tech. Her email address is [email protected].
Anne R. Driscoll
Dr. Driscoll is an Assistant Professor of Practice in the Department of Statistics at Virginia Tech. Her email address is [email protected].
William H. Woodall
Dr. Woodall is a Professor in the Department of Statistics. He is a Fellow of ASQ. His email address is [email protected].
G. Geoffrey Vining
Dr. Vining is a Professor in the Department of Statistics. He is a Fellow of ASQ. His email address is [email protected].
