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Departments: SPC Guide

Photo: Michael J. Cleary, Ph.D.


What np Charts Can Tell You
Hy Sedrate addresses on-time delivery of medications.

Michael J. Cleary, Ph.D.


Hy Sedrate, director of quality for St. Recover in the Longrun Hospital, has been worried about his organization's future and, more specifically, about his own. Through a series of complex arrangements, St. Recover has been acquired by Santa Cura Hospitals, a large regional organization made up of some two dozen hospitals and clinics.

Sedrate has learned to manage quality systems at St. Recover--but only through the prowess of his SPC team, which works nonstop analyzing hospital data.

Sedrate knows that he won't be promoted to the larger organization without a dramatic demonstration of quality improvement in his organization. The alternative is grim because there are apparently plenty of other quality directors in the same position within the Santa Cura system.

After walking around the hospital and considering the possibilities, Sedrate determines that a highly visible project he's capable of supervising concerns the number of medications that are either incomplete or inaccurate when they're delivered from the pharmacy.

"Prescription drugs are always in the news," he muses, "so everyone will notice our improvement."

With that confidence, he arranges for the pharmacists to gather data relating to missed medications. Sedrate knows he'll have plenty to work with because the pharmacy has been collecting data for the Joint Commission on Health Care Accreditation. He decides that the data should be considered as attributes data because he'll be measuring nonconforming items, defined as those medications that fail to be delivered on time. Further, he believes that an np chart is the appropriate way to analyze the data because, in effect, he'll be examining the number of deliveries with mistakes.

He develops the chart below, based on the data provided by the pharmacists.

However, when Sedrate analyzes the chart, he's disappointed that the system seems to be in control. "I was hoping to see lots of out-of-control points so we could eliminate special causes," he mutters to himself, deciding that the np chart gives him nothing dramatic with which to enhance his portfolio in the hospital. He's so worried that he finds himself losing sleep at night. Is his anxiety merited?


Sedrate's high blood pressure is pointless because the pharmacy process gives him plenty of opportunities to improve quality. The point is not just to identify out-of-control conditions but to improve the process. The np chart reflects that the process is now generating an average of 10.2 nonconformities per week.

By brainstorming and using cause-and-effect analysis, Pareto diagrams and other problem-solving and data-analysis tools, Sedrate's improvement team can identify ways to further reduce the number of missed prescriptions.



Quality improvement isn't simply gathering data but analyzing data and organizing it in order to determineways to improve a process. The plan-do-study-act cycle focuses on continuously examining processes in order to bring them to even greater levels of predictability.

About the author

Michael J. Cleary, Ph.D., is a professor emeritus at Wright State University and founder of PQ Systems Inc. He has published articles on quality management and statistical process control in a variety of academic and professional journals. His Web site is www.pqsystems.com. Letters to the editor regarding this column can be e-mailed to letters@qualitydigest.com.