[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: More on Statistics
In my opinion the lab should use a true Shewart Control Chart, obtain
at least 30 independent data points, determine the true UCL and LCL,
based on the appropriate equations, and then use these Control Limits
to determine when the process is out of control. A true Shewart
Control Chart is based on normal tendency, which results in 99.97% of
true normal data falling within +/- 3 sigma. If the data collected
falls within what is expected, 1 sigma, 2 sigma and there is no
hugging either the UCL or LCL, then all is well.What this lab appears
to be doing is setting an administrative limit using +/- 2 sigma.
This is not a statistical methodology, and therefore, no statistical
basis that they can rest on.
------------------------------------------------------------------------
Sandy Perle Tel:(714) 545-0100 / (800) 548-5100
Director, Technical Extension 2306
ICN Worldwide Dosimetry Division Fax:(714) 668-3149
ICN Biomedicals, Inc. E-Mail: sandyfl@earthlink.net
ICN Plaza, 3300 Hyland Avenue E-Mail: sperle@icnpharm.com
Costa Mesa, CA 92626
Personal Website: http://www.geocities.com/scperle
ICN Worldwide Dosimetry Website: http://www.dosimetry.com
************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html