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Cpk Calculation
We report Cpk monthly for our process. In order to report the Cpk, we must have at least 25 data points on the chart (say Xbar-R chart). But sometimes volume in certain month is so low that we won't be able to get 25 points on the chart. Is it right to calculate Cpk even though my data point is less than 25 or should I get previous month data with the current month in order to make it 25?
We report Cpk monthly for our process. In order to report the Cpk, we must have at least 25 data points on the chart (say Xbar-R chart). But sometimes volume in certain month is so low that we won't be able to get 25 points on the chart. Is it right to calculate Cpk even though my data point is less than 25 or should I get previous month data with the current month in order to make it 25?