Re: [Phys-l] Another uncertainties question...

[Ludwik Kowalski <kowalskil@mail.montclair.edu>]

The proper way to report the "non-detect" would be to specify the upper  
limit, for example, "less than A." The upper limit should ideally also  
be specified in terms of the mean value and standard deviation. But  
this is often not easy. In practice  the A is set up more or less  
arbitrarily, I suspect.
Ludwik

On Jan 25, 2008, at 12:36 PM, Jason Alferness wrote:

> (Sorry for a cross-post...)
>
> So -- awhile ago, I ran into another problem regarding uncertainties.
>
> For some groundwater contamination, a friend had to compute a weighted
> average of some values over times and locations.  Some values were  
> given
> as standard (value ± uncertainty) or equivalent, which is of course
> straightforward enough.  But the question I wasn't sure about was how  
> to
> deal with the non-detect results... Often they were reported as
> something like: "Less than xxx ppm" or somesuch...
>
> Is there a standard accepted way to deal with non-detects?  It seems  
> not
> quite correct to do any of the following: Ignore it, call it zero, use
> the threshold detect value, or to use the threshold detect as the
> uncertainty for either.
>
> Anybody had a similar experience or know what accepted procedure is?
>
> Jason Alferness
>
> --  
>
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> Jason Alferness
> University of Washington
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_______________________________________________________
Ludwik Kowalski, a retired physicist
5 Horizon Road, apt. 2702, Fort Lee, NJ, 07024, USA
Also an amateur journalist at http://csam.montclair.edu/~kowalski/cf/