Basic black (belt): Dinah Thyrst dreams of expanding her wardrobe
enews
When Shewhart introduced X-bar and R charts, it was not because they represented the most statistically efficient approach, but rather because they are mathematically easier to create. When PQ Systems' original SQCpack was created by Sean Cleary in 1982 at the age of 15, I felt as a statistician, that X-bar and S charts would soon have standard use, since computers can create them as easily as X-bar and R charts. What I did not take into consideration, however, was the power of tradition in determining usage. Grant and Leavenworth and other statisticians including myself continued to promote the application of X-bar and R charts, and as a result they have maintained their general usage in SPC. Indeed, the approach is robust enough to be useful to most applications, but in the meantime the potential offered by X-bar and S charts has been largely overlooked.