Asymmetric control limits for small samples |
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Authors: | Berna Yazici Betül Kan |
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Institution: | (1) Department of Statistics, Anadolu University, 26470 Eskisehir, Turkey |
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Abstract: | When designing control charts, it is usually assumed that the measurement in the subgroups are normally distributed. The assumption
of normality implies that the control limits for a chart for sample averages will be symmetrical about the centerline of the
chart. However, the assumption of an underlying normal distribution of the data may not hold in some processes. If the measurements
are asymmetrically distributed then the decision maker may choose different actions. One thing that can be done is to consider
the degree of skewness. If the nature of the underlying distribution is skewed, then the traditional Shewhart individuals
chart may not be valid. This paper presents a technique for constructing appropriate asymmetric control limits when the distribution
of data cannot be assumed to be a normal distribution. Meanwhile, it proposes a skewness correction method for the generated
Burr, lognormal and exponential distributions. Some numerical calculations are generated for n = 2, 3, 4 by using MATLAB. |
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Keywords: | Control charts Non-normality Skewness correction (SC) Individuals control charts (I Chart) Skewed distributions |
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