ENBIS: European Network for Business and Industrial Statistics

Variable Sample Size and Sampling Interval Cause-Selecting Control Charts

23 September 2009, 11:35 – 11:55

Abstract

Submitted by

Rassoul Noorossana

Authors

R. Noorossana and M.Shekary

Affiliation

Iran University of Science and Technology

Abstract

Abstract: The cause selecting-control chart is an effective statistical process control tool for monitoring and detecting shifts in a process having dependent steps. In this article we contemplate the statistical adaptive process control scheme for two dependent process steps. We present two variable sample size and sampling interval (VSSI) Zx and Ze control charts in order to monitor variable quality characteristics which are produced by the first process and second process steps, respectively. In this process control scheme the next sample size and sampling interval is based on the previous sample statistics. The performance of the proposed VSSI control charts is measured by adjusted average time to signal (AATS) derived by using a Markov chain approach. We demonstrate that when we use the proposed scheme to monitor two process steps, we can quickly and effectively discern which process step shifts to an out of control state. Numerical results illustrate that the performance of the proposed adaptive charts is superior to the fixed sampling policy cause-selecting control charts.
Key Words and Phrases: Adaptive sample size and sampling interval, Control charts, Cause-selecting, Dependent process steps, Statistical process control

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