Six Sigma Overview
1.1 What is Six Sigma?
Sigma ( σ) is a letter in the Greek alphabet that has become
the statistical symbol and metric of process variation. The
sigma scale of measure is perfectly correlated to such characteristics
as defects-per-unit, parts-per-million defectives, and
the probability of a failure. Six is the number of sigma measured
in a process, when the variation around the target is
such that only 3.4 outputs out of one million are defects under
the assumption that the process average may drift over the
long term by as much as 1.5 standard deviations.
Six Sigma may be defined in several ways. Tomkins (1997)
defines Six Sigma to be “a program aimed at the near-elimination
of defects from every product, process and transaction.”
Harry (1998) defines Six Sigma to be “a strategic initiative
to boost profitability, increase market share and
improve customer satisfaction through statistical tools that
can lead to breakthrough quantum gains in quality.”
Six Sigma was launched by Motorola in 1987. It was the
result of a series of changes in the quality area starting in the
late 1970s, with ambitious ten-fold improvement drives. The
top-level management along with CEO Robert Galvin developed
a concept called Six Sigma. After some internal pilot
implementations, Galvin, in 1987, formulated the goal of
“achieving Six-Sigma capability by 1992” in a memo to all
Motorola employees (Bhote, 1989). The results in terms of
reduction in process variation were on-track and cost savings
totalled US$13 billion and improvement in labor productivity
achieved 204% increase over the period 1987–1997
(Losianowycz, 1999).
