Individuals Control Charts and Levey-Jennings Charts

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Thanks so much for reading our publication. We hope you find it informative and useful. Happy charting and may the data always support your position.


Dr. Bill McNeese
BPI Consulting, LLC

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Comment (1)

  • rbarJanuary 4, 2022 Reply

    I would like to add the following:

    To my knowledge, labs often use the global standard deviation to chart and monitor the performance of Quality Control samples, hence of an analytical method. The NORDTEST Report 569 ( Version 5.1, 2018, available in the web) for environmental laboratories use a Levey-Jennings chart for control samples and a Range-chart to monitor method repeatability only when control samples or test samples are tested in replicates. Westgard rules which are widely used in clinical/medical labs are also all based on the global standard deviation (Levey-Jennings charts). It seems to me that the global standard deviation is perceived as representing better the variation of an analytical method applied in real-life circumstances.

    It seems to me that the X-mR chart, like Shewhart charts, are ideally suited to evaluate a manufacturing process whereby simple items are made sequentially or continuously in a production line. In the pharmaceutical industry, batches of a drug product are made one after the other, but with varying time durations in between (days, weeks or even months) and varying lots of same ingredients. Under these conditions, industry experts have recommended to use only the global standard deviation, because this captures better the long-term variation of the real process ( i.e. Levey-Jennings chart) and thus, lowers the rate of false alarms (See: An Industry Position Paper with Example Plan, BioPhorum Operations Group (2014), Chapter 12, P. 84,

    So, I would say that the need to adjust SPC rules to real-life data – laboratory or process data- is worth considering.

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