P Chart Sample Size
February 2, 2005 at 3:15 pm #38267
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I’m constructing a control chart where I’m tracking the number and results of electrical tests during manufacturing. My entire population size is 20 – 30 tests per month and the outcome of the test is pass/fail (attribute). My question is this: what is the minimum sample size for a p chart? I have a copy of the Western Electric book and I’m looking at Part A on Process Control Charts and the only reference I can find on sample size for a P control chart does set a lower limit on the sample size.
I have a colleague that wants control charts to be more responsive to changes in the process as it happens on the manufacturing floor — I also agree, buy this would mean posting the data every week instead of every month. Doing this would lower my sample (population) size to about 7 tests per week. My position is that such a small sample size would very sensitive to just one failure.
Jimbo0February 2, 2005 at 6:59 pm #114370
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