Dr. Walter A. Shewhart
, the father of Statistical Process Control
, 11 March 1891 - 11 March 1967
"We are not concerned with the functional form of the universe, but merely with the assumption that a universe exists." - Statistical Method from the Viewpoint of Quality Control, Dr. Shewhart
Shewhart was, in many ways, a fairly unremarkable
fellow. He is hardly well known outside of the field of statistics, despite the sheer beauty
of his work. However, his theories defined an entire branch of statistical thought which have affected the entire world.
Having studied physics
at the University of Illinois
and University of California
, the 1920s
working for the Bell Telephone Laboratories
on the Western Electric Company
's manufacturing problems. Every signal that the process was not completely uniform was acted upon, which just made things worse
. From his experience with this factory process, Shewhart developed the basics of SPC
- assignable causes and normal causes, control charts
, and the Western Elecric Zone Tests
Shewhart distinguished between common causes, the natural variability of any process, and assignable causes, hiccups in the process which are economically reasonable to seek out and eliminate. Western Electric
's mistake was that common causes were being treated as assignable causes - money and effort was wasted adjusting the process. They needed some way to decide whether a change in their product was a normal, common variation that they could ignore, or a sign of a deeper problem.
Shewhart developed ways of thinking about data which led to ways of treating data which allowed process managers to make this determination. By applying these methods to a process constantly (not just when problems appeared), it is possible to reign a process into a state of control and keep it there. Properly done, this is not only very feasible economically
, it can result in great reductions in overall costs while simultaneously improving the product.
As shown by the quote above, the robust
nature of Shewhart's work is truly amazing. His control charts are capable of taking measurements from a process which is already out of control and does not necessarily even come close to a normal distribution
and still effectively function. Even if the assumptions he based his theories on are violated, they still work! Imagine if Descartes
had said "I think, therefore I am... but even if I'm not, it wouldn't matter."
Unfortunately, Shewhart's ideas did not catch on in his native country very quickly. His colleague, W. Edwards Deming
, eventually despaired of getting SPC to work in America, and took his work to Japan
in 1949 as part of a post-war reconstruction program. So great was his success, that it is widely acknowledged that Shewhart's work was a direct cause Japan's emergence as an economic powerhouse. When applied at all levels within a company, Shewhart and Deming's techniques were revolutionary.
Shewhart also did work in operationalism
and edited the Wiley Series in Probability and Mathematical Statistics
for quite some time, but his major contribution to the world was clearly statistical process control
, for which he received numerous awards and recognitions.
By all accounts, Shewhart was a very polite and agreeable
man, seeking only to further human understanding, and hoping that his ideas would prove useful and be built upon by future generations. Considering how vital SPC is to modern manufacturing and the number of mathematicians who have followed in his footsteps, his hopes were clearly fulfilled.
Wheeler and Chambers, Understanding Statistical Process Control