Statistics
The objective of all improvement projects should be to improve the overall process. Everything else should be secondary to this objective. If you improve the efficiency of a support process, or even a portion of the core process, but at the same time lower the efficiency of the overall process,…
Recently, I wrote about the process capability index and tolerance interval. Here, I’m writing about the relationship between the process capability index and sigma. The sigma number here relates to how many standard deviations the process window can hold.
A +/– 3 sigma contains…
The four common capability and performance indexes collectively contain all of the summary information about process predictability, process conformity, and process aim that can be expressed numerically. As a result, any additional capability measures that your software may provide can only…
In May 1924, Walter Shewhart wrote a memo that contained the first example of a process behavior chart (i.e., a “control chart”). It was a chart for individual values that would be known today as a p-chart. Shewhart’s insight was that “three-sigma” limits will filter out virtually all of the…
Walter A. Shewhart is lauded as the Father of Statistical Process Control (SPC) and is perhaps best remembered for the SPC control chart. The first record of Shewhart’s control chart is found in a Bell Telephone Laboratories internal memo from May 16, 1924, making today the 100th anniversary of…
One hundred years ago this month, Walter Shewhart wrote a memo that contained the first process behavior chart. In recognition of this centennial, this column reviews four different applications of the techniques that grew out of that memo.
The first principle for interpreting…