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Control charts for monitoring the ratio of two Poisson rates
Author(s) -
Yamauchi Tsubasa,
Lee Ho Linda
Publication year - 2020
Publication title -
quality and reliability engineering international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.913
H-Index - 62
eISSN - 1099-1638
pISSN - 0748-8017
DOI - 10.1002/qre.2567
Subject(s) - ewma chart , control chart , statistics , poisson distribution , x bar chart , control limits , mathematics , statistical process control , chart , computer science , process (computing) , operating system
Abstract In this paper, we are concerning in monitoring the ratio ρ of two Poisson rates by control charts. Let X and Y be two independent Poisson random variables with means λ 1 and λ 2 = λ 1 / ρ , respectively. The study considers that only individual observations X i and Y i are available at each sampling time i . The performance in detecting shifts on the ratio ρ using several statistics, some based on normalized transformations, is evaluated by an extensive simulation study. Two types of control charts, Shewhart and exponentially weighted moving average (EWMA), are considered. The one‐sided control chart with upper control limit (UCL) is applied so that we are focusing on detecting when the ratio ρ shifted to higher rate in this paper. The results pointed out that EWMA control chart is a better alternative. Some guidelines indicating which statistics yield best performance are proposed for the practitioners.