RE: MDA vs. Critical level for DOE Free Release surveys

["Richard Orthen" <rorthen@EARTHSCIENCES.NET>]

Tom,



You're on the right course.  In a nutshell, never compare a sample result to

the MDA; always compare to the decision (critical level, DL or CL).  This is

the mantra of MARLAP and good health physics practice.  As Dan Strom put it:

"The MDA is really the 'if-it's-in-the-sample-you're-likely-to-detect-it"

level, while the DL is the

'if-you-got-a-result-above-this-it's-probably-real' level."  For the rest of

the story, see http://www.pnl.gov/bayesian/Strom/Stat-CEL-DJStrom.pdf



Cheers.



Rick Orthen

Sr. Project Manager

Earth Sciences Consultants, Inc.

Export, PA

rorthen@earthsciences.net



"The best way out is always through."

-Robert Frost



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

From:	owner-radsafe@list.vanderbilt.edu

[mailto:owner-radsafe@list.vanderbilt.edu] On Behalf Of Goff, Tom

Sent:	Tuesday, October 28, 2003 2:27 PM

To:	''RadSafe Send Message'

Subject:	MDA vs. Critical level for DOE Free Release surveys



> 	Title:

>

> 	We are discussing using a critical level for free release surveys.

> Please provide answers to the following:

>

> 	Are you using critical value or MDA for free release surveys of

> materials from your site?

>

> 	Does anyone have a reference/regulatory standard on whether to use

> MDA or critical value for free release surveys?

>

> 	Given that an MDA results in a 95% confidence in detecting

> contamination at the MDA value, what is the corresponding confidence if

> using the critical level?

>

> 	I would welcome any other comments or thoughts on this.

>

> 	Tom Goff







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