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SPC: Not Just for Manufacturing

Nicole Radziwill

Wouldn’t it be nice to catch quality or safety issues before they generate defects, incidents, injuries? Using Statistical Process Control (SPC), this can be a reality.

By Nicole Radziwill

Although random variation in a process is to be expected, “special causes” for variation -- like a machine that needs to be recalibrated, or an operator who needs additional training -- should be addressed as soon as possible. SPC is a mathematical method dating back to the 1920’s that provides an “early warning system” when a process starts to drift away from its performance targets.

But an early warning will only be beneficial if you can act on the signal it provides -- and follow through with actions to restore the system to order. Managing the response to a quality event like an early warning is something that Intelex systems do well.

The mathematical method used in SPC is based on the probability that a random process will behave a certain way. For example, think about flipping a coin. There’s a 50% (0.5) chance that the coin will come up heads, and a 50% chance it will come up tails (if it’s a fair coin). To determine the probability that the coin will come up heads twice in a row, we use the multiplication rule: 0.5 x 0.5 = 0.25, or a 25% chance. Using the same approach, the chance that the coin will come up heads three times in a row is 0.5 x 0.5 x 0.5 = 0.125 (12.5%), four times in a row is 6.25%, and five times in a row is just over 3%.

Getting five or more heads in a row is pretty uncommon -- and will only occur by chance 3 or fewer times out of every 100 opportunities, if the coin-flipping process is truly random. As a result, one of the common “run rules” is to declare a process “out of control” when there is a trend of 6 points in a row increasing or decreasing. Although there are additional run rules that can be applied, they were all devised using a similar probabilistic argument.

In December 2018, Intelex partnered with InfinityQS, a leader in data-driven manufacturing quality, to unite the early warning system of SPC with the Intelex management system -- that helps you keep track of the activities that need to be coordinated when special cause variation is observed.

SPC is a true EHSQ tool, because it can also be used illuminate health and safety issues before they lead to noncompliance or disaster. For example, you can track time series of environmental variables like emissions, or metrics like days since last incident or days since a “never event” (in healthcare). If the variable you’re measuring is showing patterns that can not be attributed to random, expected variation, the early alert can accelerate your response.

Additional Reading

Gaddis, S. (2018). Unleash a Better Safety Culture by Controlling Process Variability. Intelex Insight Report. Available from

Intelex. (2018, Dec 4). Intelex partners with Quality & SPC Leader InfinityQS to deliver the most comprehensive cloud Quality Management System.

McLean, D. (2018, July 19). Tightening Processes is Key to Worker Safety. Available from

About the Author: Nicole Radziwill Quality Practice Lead

Nicole Radziwill is the Quality Practice Lead at Intelex Technologies. Before Intelex, she was an Associate Professor of Data Science and Production Systems, Assistant Director (VP) End-to-End Operations at the National Radio Astronomy Observatory (NRAO), and manager and consultant for several other organizations since the late 1990's bringing quality management to technologically-oriented operations. She is a Fellow of the American Society for Quality (ASQ) with a Ph.D. in Quality Systems from Indiana State University. Nicole serves as Editor of Software Quality Professional (SQP) journal and is a former Chair of the ASQ Software Division. She is an ASQ Certified Manager of Quality and Organizational Excellence (CMQ/OE) and Certified Six Sigma Black Belt (CSSBB).



This material provided by the Intelex Community and EHSQ Alliance is for informational purposes only. The material may include notification of regulatory activity, regulatory explanation and interpretation, policies and procedures, and best practices and guidelines that are intended to educate and inform you with regard to EHSQ topics of general interest. Opinions are those of the authors, and do not necessarily reflect the opinion of Intelex. The material is intended solely as guidance and you are responsible for any determination of whether the material meets your needs. Furthermore, you are responsible for complying with all relevant and applicable regulations. We are not responsible for any damage or loss, direct or indirect, arising out of or resulting from your selection or use of the materials.

January 03, 2019 @ 09:49 AM EST Quality

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