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risks, and identify assumptions. These requirements should seem familiar: they are all part
of the project plan in Chapter 2.

Like the CMM, the ISO standards can be abused by an organization and reduced to
bureaucracy and paper pushing. There is a great deal of pressure on many organizations to
achieve an ISO 9000 certification at any cost, since they may be ineligible for certain con-
tracts without it. However, when the standards are used properly, they can provide good
guidelines to a project manager looking to improve how her organization builds software.

NOTE
Information on ISO 9000 can be found at the International Standards
Organization web site. The URL at the time of this writing is http://www.
iso.ch/iso/en/iso9000-14000/iso9000/iso9000index.html

Six Sigma
Six Sigma is an approach to improving quality in manufacturing and business processes. It
was developed at Motorola in the early 1980s, and it has been used successfully at many
software organizations. The goal of Six Sigma is to produce a product of consistent quality
by statistically measuring the defect rate, improving the processes to eliminate those
defects, and then monitoring the improvements. Six Sigma has been used to successfully
improve organizations in many industries. While it has a reputation for success in large
companies with thousands of employees, Six Sigma can be applied to small project teams
as well.
The Greek letter sigma refers to standard deviation—Six Sigma means “six standard devia-
tions from the mean.” To achieve this level of quality in a manufacturing process, 99.
9997% of all products must be of acceptable quality (or 3.4 defects per million opportuni-
ties). It’s not hard to get an intuitive grasp on what this means in the real world. Accord-
ing to Jeannine Siviy at the Software Engineering Institute, a Four Sigma level of
quality—meaning that we’re 99.9% sure—would yield:

• 9 hours of unsafe drinking water a year
• 107 incorrect medical procedures a day

• 200,000 incorrect drug prescriptions a year
• 18,322 pieces of mishandled mail an hour

• 2,000,000 documents lost by the IRS a year
• Two short or long landings at any major airport a day
Variance is an important part of Six Sigma. There is a saying at General Electric, an early
adopter and innovator in the Six Sigma world: “Our Customers Feel the Variance, Not the
Mean.” All processes have some inherent variability. No process, especially not a software
process, produces defects at an entirely regular rate. What GE found is that customers can
get used to a “noise level” of defects; it’s the large changes in quality that will really get

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