Learn in the textbookManagement Techniques for Quality and Process Improvement (TQC, TQM, Six Sigma, TOC)
DefinitionSix Sigma (シックスシグマ) is a quality improvement method that captures the results of products or work as measurements and reduces defects by statistically shrinking their variation.
ExplanationVariation is how far results drift each time even when the same work is repeated, and statistics expresses it with the Greek letter σ (sigma, the standard deviation). The 6σ in the name comes from the goal of holding variation down so far that defects stay at a few per million opportunities. Improvement can proceed, for example, through the sequence called DMAIC: define, measure, analyze, improve and control.
AnalogyIf the bread you bake each morning swings widely in weight from day to day, you log the flour and the oven temperature, track down the cause and get every batch to come out the same weight.
Memory hookThe σ in the name is the statistical symbol for standard deviation, so the name itself tells you this method speaks about quality in data.