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A Robustness Study of Charts with Variable Sampling Intervals

Summary: Recent theoretical studies have shown that, for all but very large process shifts, control charts using variable sampling interval (VSI) schemes are more efficient in their detection of shifting processes than the more conventional fixed sampling interval (FSI) schemes. This article, through simulation, considers the properties of the VSI chart in an environment where the process data are not normally distributed but are contaminated. In addition, it evaluates the behavior of VSI charts where a trimmed mean, a winsorized mean, or the median is used as the chart statistic. Comparisons between the FSI and VSI charts indicate that the VSI chart continues to be more efficient. Further, trimming the mean and/or including a rule for reducing the amount of switching between the two different sampling intervals improves the efficiency.

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  • Topics: Sampling
  • Keywords: Sampling interval,Average time to signal,Simulations,Switching rules
  • Author: Amin, Raid; Miller, Richard
  • Journal: Journal of Quality Technology