Noted Quality expert Joseph Juran has criticized Six Sigma as "a basic
version of quality improvement", stating that "[t]here is nothing new there."
Studies that indicate negative effects
caused by Six Sigma
A Fortune article stated that "of 58 large companies that have
announced Six Sigma programs, 91 percent have trailed the S&P 500 since." The
statement is attributed to "an analysis by Charles Holland of consulting firm
Qualpro (which espouses a competing quality-improvement process)." The gist of
the article is that Six Sigma is effective at what it is intended to do, but
that it is "narrowly designed to fix an existing process" and does not help in
"coming up with new products or disruptive technologies." Many of these claims
have been argued as being in error or ill-informed.
A Business Week article says that James McNerney's introduction of Six Sigma
at 3M may have had the effect of stifling creativity. It cites two Wharton
School professors who say that Six Sigma leads to incremental innovation at the
expense of blue-sky work.
Based on arbitrary standards
While 3.4 defects per million might work well for certain products/processes,
it might not be ideal for others. A pacemaker might need higher standards, for
example, whereas a direct mail advertising campaign might need lower ones. The
basis and justification for choosing 6 as the number of standard deviations is
not clearly explained.