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Normal control charts with nonparametric Willem Albers and Wilbert C.M. Kallenberg

Summary: Normal control charts with nonparametric
Willem Albers and Wilbert C.M. Kallenberg
Department of Applied Mathematics
University of Twente
P.O. Box 217, 7500 AE Enschede
The Netherlands
Abstract Parameter estimation causes a considerable stochastic error in standard She-
whart charts. This problem can be solved using suitable correction factors. But if the
normality assumption itself fails, in addition a nonvanishing model error will occur. By
then, a nonparametric alternative, such as the recently proposed MIN chart, might be a
better idea throughout. However, for those reluctant to give up on the Shewhart chart, a
third possibility is offered here. One sticks with this traditional chart as long as the data
suggest that the resulting model error is acceptable. Only if this not the case, the MIN
chart kicks in and as such serves as a nonparametric safeguard.
Keywords and phrases: Statistical Process Control, Phase II Control Limits, Minimum,
2000 Mathematics Subject Classification: 62 G 32, 62 P 30
1 Introduction and motivation
When using standard Shewhart X control charts, it is typically assumed that the ob-


Source: Al Hanbali, Ahmad - Department of Applied Mathematics, Universiteit Twente


Collections: Engineering