RE: Control Charts for Alpha Counters

["MacLellan, Jay A" <jay.a.maclellan@pnl.gov>]

Chris Hofmeyr wrote "If one can be confident that the background is also Poisson
distributed, it is a big advantage.  The beauty of a Poisson distribution is of
course that the average is equal to the variance..."

I agree with everything you say.  I just want to emphasize that the true
variance equals the true mean, but you don't have a good estimate of the
variance without a good estimate of the mean.  If you establish a control chart
based on the variance of an inadequate sample population, you may be setting
yourself up for trouble.

Just my opinion.

Jay A. MacLellan, CHP
Radiation and Health Technology
Pacific Northwest National Laboratory
Phone:  509-376-7247
Fax:      509-376-2906
Email:   jay.a.maclellan@pnl.gov

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