Computing Upper and Lower Control Limits

Computing Upper and Lower Control Limits
Message posted by Arlene on October 7, 1999 at 12:00 AM (ET)

I would like to know how to compute the upper and lower control limits for data.
Any help will be appreciated.

Thanks

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Re: Computing Upper and Lower Control Limits
Message posted by JG on October 7, 1999 at 12:00 AM (ET)

For control limits you usually assume a normal distribution - if you ara tracking a mean or average.

Generally you set the limits at +/- 2 or 3 standard deviations around the true mean or longterm sample average, etc.

An equivalent procedure is to simply plot the cumulative average as see how it behaves.

If you are interested in other statistics, there are equivalent procedures based on the appropriate sampling distribution.

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