Variation is at the heart of most quality problems!


The Heart of Statistical Process Control (SPC)

  • Variation exists in everything.
  • When we’re manufacturing products for customers who expect and demand high quality and consistency in our goods, variation can become a big problem.
  • Too much variation leads to rework, scrap, or customer problems.
  • A perfect process would be one with no variation. They don’t exist.
  • As the variation in our processes is reduced, the output of our processes will be improved.  
  • That’s our primary goal with SPC:  To reduce the variation in our processes and then monitor the process to make sure the variation doesn’t increase.
The first step to using SPC is to gain a deep understanding of the variation in your process.  

Measuring Variation

You can measure variation visually using a histogram or you can measure it mathematically using statistics.  Statistics give you a more precise measure of variation, but don't discount the value of actually "seeing" the variation in your process.

A histogram can tell you if there is a LOT of variation or a little, what the pattern is and if there is anything unusual about the data.

With a better understanding of the variation in your process, you can decide if you need to reduce the variation, address unusual patterns of the variation or if you simply need to monitor it to make sure it stays in check.  In all likelihood, you will be doing some of each.

What are Control Charts?

Control charts are a tool to help monitor the variation in a process.  They give a statistical signal that a process has gone out-of-control so the operator can make the necessary adjustments to bring the process back into control.
  • The chart itself can’t control the process. The control chart provides a signal so the operator can take action on the process.

A process that is stable is in-control. If the process changes, we get a signal from the control chart that it has gone out-of-control.  Adjusting a process when it is not statistically out-of-control is considered over-adjustment and actually results in increased process variation. Control charts can be used to measure product characteristics or in-process parameters.
  • Measuring an in-process parameter is the best way to monitor a process because it may provide a signal that the process is going out-of-control before bad product is made.

Helpful Resources On Statistical Process Control


SPC Training for Your Team

With our online SPC Training courses, your team will get detailed instruction not only on how to use a control chart, but on what the chart is telling them.  

Master Courses - $69 each

Basic SPC
Advanced SPC
Basic SPC for Business Processes

Targeted Training Courses - $34.50 each

Understanding Variation
Using Control Charts
Process Capability Basics
Advanced Control Charts
Advanced Process Capability

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