More on Statistics

["Redmond, Randy R. (RXQ) " <RXQ@y12.doe.gov>]

I'd like opinions and definitely some references which justify the following
practice or show that the following practice is not correct.  

A laboratory performs a yearly calibration on its low level alpha counters.
During the yearly calibration, backgrounds are taken for various counting
times (10 each; average used for the background) - 60, 30, 20, 10, 5, 2, 1,
0.5 minutes.  The lab performs a daily background consisting of  10, 2
minute counts.  A control chart consisting of the daily 2 minute backgrounds
versus the yearly 2 minute background +- 2 standard deviations is kept  (if
the daily background falls outside yearly +- 2 std.dev. something is wrong).
The yearly backgrounds are used to document the MDAs of the instruments and
to determine the sample critical levels.  The daily background is subtracted
from all sample results regardless of sample count time.

Randy Redmond
Lockheed Martin Energy Systems
P.O. Box 2009
Bldg.  9769,  MS 8081
Oak Ridge, TN  37831-8081
Email:  rxq@y12.doe.gov
Phone:  423-574-5640
Fax:  423-576-6047

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