[R-sig-eco] Which function would fit these data (Version 2)

Bob O'Hara bohara at senckenberg.de
Fri Apr 13 08:37:03 CEST 2012


On 04/13/2012 06:16 AM, Beutel, Terry S wrote:
> Hi list members
>
> Sending this again as symbols in the previous version did not translate.
>
> Apologies if this is not too specifically R related, but I am looking fit a model to some simulated data. X is distance to sample point, y is binary outcome (present/absent). I was hoping someone can suggest a (presumably) non linear function that might meet the following criteria
>
> A.   0<= y<=1 (actual responses are binary)
> B.   xmax = infinity
> C.   xmin<= 0
> D.   Where x = 0 then y>= 0
> E.   Where x equals Infinity then y equals 1
> F.   As x approaches Infinity from xmin, the slope of the function declines monotonically toward 0.
my initial reaction was to think "logistic regression", but  my 
experience with questions like this is that we'll save a lot of time if 
you explain the context.

BTW, I'm not sure why you want "the function" to decrease to zero when x 
approaches infinity when at the same time y should equal 1 at infinity. 
It's not a big problem, though. Just use 1-y instead of y.

Bob


-- 
Bob O'Hara

Biodiversity and Climate Research Centre
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