RE: Type II Poisson Errors (REPOSTED)

[Tom Morgan <tmorgan@ISOTOPEPRODUCTS.COM>]

Yes, Chapter 9 of Herman Cember's book Introduction to Health Physics has a

discussion of Type I and Type II errors as they relate to LLD.



-----Original Message-----

From: james.g.barnes@ATT.NET [mailto:james.g.barnes@ATT.NET]

Sent: Friday, September 21, 2001 10:45 AM

To: radsafe@list.vanderbilt.edu

Cc: james.g.barnes@BOEING.COM

Subject: Type II Poisson Errors (REPOSTED)





PLease forgive me if this is a repost.  I am in the 

process of shifting email accounts, and the first posting 

may have been lost in the shuffle. . . .



Folks,



We have been working with determining detection levels in 

some low background count situations, and have been 

examining the counter behavior using Poisson statistics.  

Poisson statistics will basically allow one to calculate 

a cumulative probability of the number of counts a person 

would see for a given count with an expected background 

for that count period.  This approach appears to 

calculate a value that could be considered (I suppose) 

equivalent to a "Type 1" scenario (i.e., roughly 

equivalent to the Decision Level; prone to "false 

positive" detections).



Is there an approach using a poisson distribution that 

calculates something akin to the Type II error (i.e, the 

LLD value that anticipates and corrects for false 

positive events).  I have looked at all the usual 

references, but haven't seen any treatment of this.  Is 

"LLD" even a meaningful concept in a Poisson 

distribution?



Thanks,



Jim Barnes, CHP

Radiation Safety Officer

Rocketdyne/Boeing

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