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List:       sas-l
Subject:    Re: Figuring distances - thanks and comments
From:       John Whittington <John.W () MEDISCIENCE ! CO ! UK>
Date:       2002-10-31 23:13:01
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At 13:15 31/10/02 -0500, Peter Flom wrote:

>Certainly there are many people here who inject and don't go to
>exchanges.  And very few go any distance to get needles.  But we are
>looking at a different question: Our key question is What influence when a
>city gets a syringe exchange program.  It doesn't take many people to
>start a program, so even if only one is influenced by having one 100 miles
>away, that's important to know.

Fair enough.  In fact, it now occurs to me that you may actually be
thinking of an opposite sign to this effect than what first occurred to
me.  I was thinking that the assumption was that if there were already a
needle exchange program 'not far away', then that would be an argument
against setting one up (but would invoke the practicalities I've been
discussing of how far addicts could reasonably be expected to
travel).  However, maybe you're thinking that the presence of an existing
program in a place 'nearby' might actually 'inspire' or 'encourage' a city
to set up a program ("if they've got one, we should have one too"!).

>As to 'N within 100 miles' being arbitrary, I agree.  And it is
>problematic that having 5 within 10 miles would count the same as 5
>within 100.  I am not set on this solution, by any means.  ... I would be
>open to other indexes, but I am not sure your idea of one based on mean
>distance is better; mostly because of the effect of large
>values on the mean.  Perhaps something based on the median would be
>good.....

Sure, as I just, I was just producing 'thoughts off the top of my
head'.    An index based on median would undoubtedly be better, for the
reason you give.  Median divided by N would give an index which rose as
accessability to programs decreased - due to smaller numbers and/or greater
distances.

Kind Regards
John

John

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