RE: Tom Ryan's reply to the SPC theory point

[Steven_S_Prevette@rl.gov]

Simplicity is fine as long as the results are reasonable, but we cannot
assume that almost everything is normally distributed, or to act as if
non-normality doesn't matter.  We don't teach statistics that way, and 
statistical methods should not be used in such a manner.

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Please review Dr. Shewhart's original work on SPC.  Control charting is
based upon the Tchebychev Inequality, and is not dependent upon
distribution.  Acheson Duncan's Quality Control and Industrial Statistics
also supports this claim.  Most courses on SPC teach it in a different (I
won't say wrong) manner (central limit theorem and normality) than Dr.
Shewhart originally intended.

Steve Prevette
QA Engineer, ESH Radiological Compliance
Fluor Hanford, A Fluor Global Services Company
ASQ Certified Quality Engineer
steven_s_prevette@rl.gov
509-373-9371