
333
33
Six Sigma
33.1 SIX SIGMA
Six Sigma (SS) methods are recognized by many companies as a means for reducing defects,
increasing company productivity, and improving company protability. The label “Six Sigma”
originates from statistical terminology. In statistics, the sigma (σ) represents standard deviation.
For a normal distribution curve, the probability of falling within a plus or minus SS from the mean
is 0.9999966. This is more commonly expressed in production processes as a defective rate for a
process, which will be 3.4 defects per million units. Thus, SS promotes high degree of consistency
by designing opera