Journal of Medical Statistics and Informatics

Journal of Medical Statistics and Informatics

ISSN 2053-7662
Original Research

Phase II Performance of P-Charts and P'-Charts

Joseph Hagan1* and Bin Li2

*Correspondence: Joseph Hagan

1. Assistant Professor, Baylor College of Medicine, Department of Pediatrics, Texas Children's Hospital - Pavilion for Women, 6651 Main Street, Houston, TX, USA.

Author Affiliations

2. Associate Professor, Louisiana State University, Department of Experimental Statistics, Room 173 Martin D. Woodin Hall Louisiana State University, Baton Rouge, LA, USA.


The p-chart has traditionally been used to monitor processes that yield binary data. The p'-chart that adjusts the p-chart control limits for between subgroup variation was proposed in 2002 in an effort to reduce the p-chart's false alarm rate in the presence of large subgroup sizes. As illustrated with an example using real pharmacy data, the p-chart and p'-chart often yield very different results and how to decide which chart is appropriate for a given situation is not clear. A simulation study was undertaken to examine the phase II performance of the p-chart and p'-chart. With large subgroup sizes or when the between subgroup variation is high, p-charts have relatively high sensitivity to detect out-of-control shifts, but exhibit a high false alarm rate when the process is in-control, while p'-charts have low sensitivity to detect out-of-control shifts but have relatively low false alarm rates. For a specific situation, Youden's index can be used to decide whether to act on p-chart or p'-chart results while considering the relative costs of false positives and false negatives.

Keywords: Statistical process control charts, p-chart, p'-chart, Sensitivity, False alarm rate

ISSN 2053-7662
Volume 6
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