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Skewed Distributions. mean = median. mean. median. median. mean. Average class shoe size – No skew. Time to drive to work – Skewed right. Hours of sleep per week – Skewed left. Standard Deviation. Standard Deviation ( σ ) = the average difference of each value from the mean. √.
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Skewed Distributions mean = median mean median median mean Average class shoe size – No skew Time to drive to work – Skewed right Hours of sleep per week – Skewed left
Standard Deviation • Standard Deviation (σ) = the average difference of each value from the mean √ Σ(x - )2 Std dev = n -1 It is a measure of how spread apart each individual data point is from the mean
What is Cp? • Cp is a measure of how well the variation in the data can fit within the tolerance limits If the variation (6σ) is less than the tolerance limits, you have acceptable variation If the variation (6σ) is greater than the tolerance limits, you have unacceptable variation LL UL LL UL 6σ 6σ
Examples USL Cpk = 0.33 15.87% Predicted failure rate -3 -2 -1 0 +1 +2 +3