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In Statistical Process Control, the Western Electric Rules are decision rules for detecting "out-of-control" or non-random conditions on control charts. Locations of the observations relative to the control chart control limits (typically at ±3 standard deviations) and centerline indicate whether the process in question should be investigated for assignable causes. The Western Electric Rules were codified by a specially-appointed committee of the manufacturing division of the Western Electric Company and appeared in the first edition of its Statistical Quality Control Handbook in 1956. Their purpose was to ensure that line workers and engineers interpret control charts in a uniform way. ==Motivation== The rules attempt to distinguish unnatural patterns from natural patterns based on several criteria: #The absence of points near the centerline (identified as a mixture pattern) #The absence of points near the control limits (identified as a stratification pattern) #The presence of points outside the control limits (identified as an instability pattern) #Other unnatural patterns (systematic (autocorrelative), repetition, trend patterns) To achieve this, the rules divide the chart into zones, measured in units of standard deviation (σ) between the centerline and control limits, as follows: Zones A, B, and C are sometimes called the three sigma zone, two sigma zone, and one sigma zone, respectively. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Western Electric rules」の詳細全文を読む スポンサード リンク
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