Sigma – an important statistic for us to know. Sigma, or the standard deviation, is a measure of how much dispersion there is in a process. There are numerous ways to estimate sigma. One way, of course, is simply to calculate the value using the formula for the standard deviation:

where X i are the individual results, X is the average and n is the number of individual results.

This is a measure of the dispersion in the data. But is it a good one to use? Does it fairly represent the data? The answer is you don’t know because you haven’t...

This is the fourth and last blog in our four-part series introducing control charts. The first blog addressed the question of what a control chart is . The second blog explored the relationship between variation and control charts . The third blog addressed the purpose of a control chart . This blog answers the following question:

Where are control charts used?

The truth is that there are...

This is the third in a four-part series introducing control charts. The first blog addressed the question of what a control chart is. The second blog explored the relationship between variation and control charts . This blog begins to answer the following question:

What is the purpose of a control chart?

We will continue with the driving to work example shown in the last two blogs to explore three different purposes for a control chart....

This is the second in a four-part series introducing control charts. The first blog addressed the question of what a control chart is . This blog will answer the following question:

What is variation and how does it relate to a control chart?

Understanding variation is the key to effectively using a control chart. A control chart provides a method for your process to communicate with you – to tell you if the process is doing what you designed it to do (only common causes of variation are...

This is the start of a four-part blog on control charts. The blogs will answer the following questions:

• What is a control chart?
• What is variation and how does it relate to a control chart?
• What is a control chart used for?
• Where is a control chart used?

Control charts are at the heart of statistical process control (SPC). So maybe we should start with answering what a process is. A process is simply what we do. It can be filling out an expense report, checking a person into a hospital, driving to work, filling a prescription, etc...