Jordan Hiller, Principal Systems Engineer, SAS
Di Michelson, Principal Analytic Training Consultant, JMP
Byron Wingerd, Principal Systems Engineer, JMP
The Levey-Jennings (L-J) chart is a variant (perversion?) of the traditional Shewhart Individuals and Moving Range (X-MR) chart. The control limits in an L-J chart are drawn using the sample standard deviation statistic for estimation of sigma, rather than the short-term estimate based on the moving range. We argue that the L-J chart is fundamentally and irredeemably flawed, and that there is always a more appropriate chart that should be used for process control. In this presentation, we review the history of the L-J chart, refute the most common justifications for its use, and provide suggestions for alternatives.
