COMMERCE 2OC3 Lecture Notes - Lecture 14: Statistical Process Control, Random Variable, Standard Deviation
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A statistical technique to ensure that processes conform to standards. The target is 100g per bag, but it is possible that you get variations. Distribution of natural variation is stable over time. When only natural variation is present, distribution stays the same. In this case, we say process is in control. Relatively strong changes, outside the stable random patterns. "assignable: in the sense that the underlying causes can be discovered and corrected. Weight of a bag of potato chips is a random variable. When assignable variation is present, distribution is unstable. In this case, we say process is out of control. Spc uses the tool control chart to detect assignable variation i. e. , to detect if the distribution is stable. The mean of the distribution is stable (by -chart) The range (a measure of validity) is stable (by r-chart) We will construct the -chart by 4 steps. Often 5 to 8 items for each sample, and use the sample average.