Mounted search and rescue

[Lois Guyon <laguyon2@yahoo.com>]

Una's analysis of the probability of detection (POD) in an area with many 
corn fields is interesting in that it points toward using assumptions.  If 
there were unlimited resources, all the fields could be thoroughly searched.  
However, most searches have more real estate to explore than there are 
searchers.  In this case, the higher probability areas were searched first.  
While the search was still ongoing at the time of the recovery.  The chance 
of the person's location being discovered in the low probability area was 
slim.  Once the search moved to the level of a probably recovery it was 
reasonable to see if farmers harvesting the corn would discover the remains. 
The assumption that the person was not in the corn turned out to be 
erroneous, but still not entirely irrational.  

Lois


--- On Mon, 10/27/08, Una Smith <una.smith@att.net> wrote:

> From: Una Smith <una.smith@att.net>
> Subject: Re: [MSAR] Midwest search
> To: "Mounted search and rescue" <msar-riders@lists.ibiblio.org>
> Date: Monday, October 27, 2008, 10:05 AM
> As a child I spent a lot of time in corn fields, playing
> hide&seek
> and looking for animals.  I don't recall corn being
> much worse than
> the tall grass hay I also played in, that gave nasty cuts. 
> Someone
> with dementia, who liked playing in the corn as a child,
> might be
> expected to go into the corn.
> 
> Irv wrote:
> >The first rule of any incident is never assume.
> 
> That's right.  The probability of the subject being in
> a given area
> (POA) does not change once an area has been searched. 
> Searching
> changes the probability of detecting the subject (POD) from
> 0 to
> some value approaching 1.  Probability of success (POS) =
> POA x POD.
> So it is a mistake to hasty search an area and declare it
> "clear",
> ie that POA = 0.
> 
> In this case, let's say the global prior probability of
> the subject
> being in a corn field is X.  But there 1000 corn fields in
> the
> vicinity of his town.  Let's say they are all equal
> area, and 
> equally accessible.  He can be in only one of them, so POA
> for each
> is X/1000.  If X is 10%, then POA is 0.1/1000 = 0.0001. 
> Not likely.
> Now consider POD.  POD is a function of search effort.  POD
> per
> groundpounder day spent in a corn field is very low,
> because the
> corn is dense and tall.  Searchers might need to walk every
> row
> or at least every other row.  A quarter mile is 1320 feet. 
> If the
> corn rows are planted 2 feet on center then there are
> 1320/2=660 
> rows and the distance to be walked between them is 660 rows
> / 4
> rows per mile = 165 miles.  To walk a single average corn
> field
> that is 1/4 mile square would take somewhere on the order
> of 20
> groundpounder days.  That is assuming a person could walk 8
> miles
> in a corn field in one day, probably a very optimistic
> assumption.
> 
> How much searcher effort would you put into searching a
> corn field
> with such a low POA?  Not much, especially when you know
> the field
> will be harvested soon, and harvesting will yield a very
> high POD
> for essentially 0 searcher effort.
> 
> To search low POA, high effort fields, I would want to use
> air
> scenting animals, dogs or horses.
> 
>       Una Smith
>       New Mexico
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