[ RadSafe ] Re: Positive predictive value of dirty bomb screening (was Cell phone automatic radiation detection)

[Clayton Bradt]

John Flood wrote:

               'Am I missing something 
or oversimplifying?  This seems to me 
to be doomed to failure because of 
nuclear medicine.  Patients moving 
around a city in essentially random 
patterns would make it impossible to 
identify one detected source as hostile 
amongst a large array of detected 
sources that are medical in nature.  
And the number of these patients will 
increase substantially as the baby-
boomer generation ages.  Discrimination 
based on photon energy won't help, 
either. '

I did a quick and dirty calculation of 
the positive predictive value of such a 
screening program for "dirty bombs" in 
NYC.  Assuming that the police pager-
type detectors are 100% sensitive to 
both dirty bomb material and nuc med 
patients, and that on any given day 
there is one dirty bomb being 
transported through the streets of NYC, 
the PPV comes out to around 10-4 to10-
5.  

For all intents and purposes, every 
hit is guaranteed to be a false 
positive.  What kind of strategy is 
this?   

It is pretty clear that either no 
forethought went into designing this 
dirty-bomb screening program, or that 
the "deciders" in charge have no 
concern about how effective it will be 
so long as it makes it appear that they 
are doing something.

BTW, if I can figure this out, so can 
UBL.

Clayton Bradt




Clayton J. Bradt
dutchbradt at hughes.net