SIX SIGMA FUNDAMENTALS - Software Design for Six-Sigma: A Roadmap for Excellence - page 150

the supporting documentation. With software, quality is measured as conformance to
expectations, availability, experience of the process, and people interacting with the
software or the IT application. 2
If we look at Figure 7.2, we can observe the customer's experience through three
aspects: (1) The specific product or service has attributes such as availability, “it's
what I wanted, it works;” (2) the process through which the product (including
software) is delivered can be ease of use or value added; and (3) the people (or
system) should be knowledgeable and friendly. To fulfill these needs, there is a life
cycle to which we apply a quality operating system.
Six Sigma is a philosophy, measure, and methodology that provides businesses
with perspective and tools to achieve new levels of performance in both services and
products. In Six Sigma, the focus is on process improvement to increase capability
and reduce variation. The vital few inputs are chosen from the entire system of
controllable and noise variables, and the focus of improvement is on controlling
these vital few inputs.
Six Sigma as a philosophy helps companies achieve very low defects per million
opportunities over long-term exposure. Six Sigma as a measure gives us a statistical
scale to measure our progress and to benchmark other companies, processes, or
products. The defect per million opportunities measurement scale ranges from 0 to
1,000,000, whereas the realistic sigma scale ranges from 0 to 6. The methodologies
used in Six Sigma build on all of the tools that have evolved to date but put them into
a data-driven framework. This framework of tools allows companies to achieve the
lowest defects per million opportunities possible.
The simplest definition of a defect is that a defect is anything that causes customer
disatisfaction. This may be a product that does not work, an incorrect component
inserted on the manufacturing line, a delivery that is not on time, a software that takes
too long to produce results, or a quotation with an arithmetic error. Specifically for
a product, a defect is any variation in a required characteristic that prevents meeting
the customer's requirements. An opportunity is defined as any operation that may
introduce an error (defect). With those definitions in hand, one might think that
it is straightforward, although perhaps tedious, to count defects and opportunities.
Consider the case of writing a specification. An obvious defect would be any wrong
value. What about typographical errors? Should a misspelled word be counted as a
defect? Yes, but what is the unit of opportunity? Is it pages, words, or letters? If the
unit is pages, and a ten-page specification has three errors, then the defect rate is
300,000 per million. If the unit is characters, then the defect rate is approximately 85
per million—a value much more likely to impress management. What if the unit of
opportunity is each word or numerical value? The defect rate is then approximately
500 per million, a factor of 100 away from Six Sigma.
Reduction of defects in a product is a key requirement in manufacturing for
which six sigma techniques are widely used. DMAIC (Define opportunity, Measure
performance, Analyze opportunity, Improve performance, and Control performance)
is a Six Sigma methodology often used in effecting incremental changes to product or
2 See Chapter 1.