Dr. Deming Tidbit - The Renaming of Chance and Assignable Correlation

Putting out fires is not improvement of the process. Neither is discovery and removal of a special cause detected by a point out of control. This only puts the process back to where it should have been in the first place. - Dr. Deming - https://deming.org/quotes/10239/

The more I study Dr. Deming, the more I find these nuggets of insight into his mind. In a previous blog post (here), I explained why Dr. Deming changed PDCA to PDSA. I've also been wondering why Dr. Deming altered the wording of Dr. Shewhart's original names for the two types of variation. The creator of Statistical Process Control (SPC), Dr. Shewhart, originally called the two types of variation chance and assignable. Later, Dr. Deming referred to the two kinds of variation as common cause and special cause.

Deming was the quintessential academic, a lifelong student and teacher who took great care choosing his words. Rather than focusing on the source of variation, he used the words common and special to emphasize the system. By observing and analyzing variation using the terms common cause and special cause, the analysis can focus on the people who are responsible for changing the system rather than examining each cause separately. In reality, an American sociologist, Harry Alpert, changed the name from chance to common in 1947. Deming may have adopted Alpert's rename. Dr. Deming, however, renamed assignable to special so that students using SPC would understand that special cause variation would not be involved with just removing the variation, but rather associate it with those best able to address the particular intervention.