Can a manufacturing quality model work for software?

Six-sigma (i.e. 6 standard deviations) is a parameter that is used in statistical models of the quality of manufactured goods (including computer hardware). It also serves as a slogan that suggests high quality. Some attempts have been made in the past to apply 6-sigma to software quality measurement. Software engineers often look to hardware analogies to suggest techniques that are useful in building, maintaining or evaluating software systems. The author explains why the 6-sigma approach to hardware quality simply does not work when applied to software quality.