RE: less than data

["Sherman, Conrad" <ShermaC@ttemi.com>]

here is how i report smear counts.

report the actual net count converted to activity 

also report the critical level and detection level.

The critical level is simply the point for which a sample with exactly that
level of activity would be identified as having activity (different from
background) one-half of the time.  If it exceeds l-c, you call it positive.

the detection level (MDA, LLD, LLC) is the point for which a sample with
exactly that level of activity would be correctly identified 95% of the
time.  The l-d is an a priori value, you use it to determine sample count
time in a particular background, and it is what you quote as your (or the
labs ) detection capability.  In your case, l-d should be between 20 and 100
dpm (10 to 50 % of standard)

Labs will quote l-d, not lc.  if you have a set of background data and
sample data, you can use l-c to decide which samples are "different" than
background, without attaching any significance to that difference.

In some cases, you can also report the maximum activity that could have been
missed  (some refer to this as r-max)

There are no regs on this That I am aware of. see the old hps guidline on
reporting environmental data, an old nureg authored by l. Curry,also Al
Brodsky wrote some articles in Health Physics for bioassay statistics, and
the NUREG 1505/1506/1507 series and MARSSIM for more information.  MARSSIM
has some equations also.

The guy who wrote you up should have explained all this.

conrad sherman


Dave Biela wrote:

> We recently got hit during a DOE audit for reporting a "less than"
number on a survey form.  For example we have a smear-able release limit
of 200 dpm/100cm-sq beta, if we see nothing, we use less than.  How do
you do it at other sites?  Have you run into the same audit comments?
Any regulatory paragraph  references would be appreciated.
>
> RADSAFE please respond directly to me at:
>
> bielad@wv.doe.gov
>
> 
************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html