A direct procedure for monitoring the coefficient of variation using a variable sample size scheme

ABSTRACT

A variable sample size (VSS) scheme directly monitoring the coefficient of variation (CV), instead of monitoring the transformed statistics, is proposed. Optimal chart parameters are computed based on two criteria: (i) minimizing the out-of-control ARL (ARL₁) and (ii) minimizing the out-of-control ASS (ASS₁). Then the performances are compared between these two criteria. The advantages of the proposed chart over the VSS chart based on the transformed statistics in the existing literature are: the former (i) provides an easier alternative as no transformation is involved and (ii) requires less number of observations to detect a shift when ASS₁ is minimized.

KEYWORDS:

• Average number of observations to signal
• Average run length
• Average sample size
• Coefficient of variation
• Variable sample size

Mathematical Subject Classification:

• Primary 90B25
• Secondary 62P30

Funding

This research is supported by the Universiti Sains Malaysia Research University grant, number 1001/PMATHS/811263.