An inaugural winner of the united states malcolm baldridge national quality
its persuit of six-sigma quality standards in everything they did-both
manufacturing and nonmanu-
facturing operations.They coined the phrase from the greek character sigma;
that statistices use to
represent units of standard deviation. Statistical tables define how much
area is under various types
of distribution curves at any distance from the mean at function of sigma.
table 8.3 option yielding process capability index=1.0
||reduce process average
||reduce process variation
|uppre control limit||18.2||18.2||14.0||14.5
Motorola adopted the most common curve, the normal distribution, as a model to define
ility of observing defects. It based its terminology on the performance
of a process with its average shifted 1.5 σ from the center between the specification
limits. Its six-sigma goal translate into
merely 3.4 defects per million
opportunities(3.4ppm),which its equivalent to 99.9997 percent per-
elegant approach enables assigning a quantitative value to process performance
without demanding a strict statistical analysis.
Progress towards the six-sigma goal can be measured by assigning an equivalent
performance level(number of sigmas) based on the measured defect rate.
For example, suppose a process is producing 62
defects per 10,000 opportunities(6,200 ppm defects).This is equivalent to
The six-sigma type of analysis is a simplified version of the previously
described process capability
index . Rather than requiring the statistical
calculation of process variation, the six-sigma type
of performance level
can simply be looked up in a table or on a graph. Furthermore, the six-sigma
type of analysis can be applied to products and services that lack physical
or chemical tolerances.