On May 17, 2012, at 3:16 AM, Beutel, Terry S wrote:
I using oldlogspline (from logspline package) to model data
distributions, and having a problem.
My data are search area sizes. They are based on circular search
radii from random points to the nearest edge of the nearest grass
tussock. Search area sizes are distributed from 0 (the random point
intercepts a tussock) and upwards (as points are further from any
tussocks). The density of all my distributions (using doldlogspline)
are highest at size=0, and decline as search area increases.
I am most interested in the probability of a value in the
distribution being equal to 0 (ie probability of a direct hit on a
tussock). I know I can just use the proportion of actual hits, but
am curious to compare this to an estimate from a density estimation.
Unfortunately when using poldlogspline, this probability is always=0
(simulated data example is below). How can this be, given that the
density is highest at area=0?
simdat<-c(rep(0,8),rexp(92))
myspline<-oldlogspline(simdat,lbound=0)
poldlogspline(fit=myspline, q=0)
[1] 0
Any help to work out the probability of an area value in my
distribution = 0 would be appreciated
Probabilities often are zero over a zero-length interval , even if
their densities are positive. Surely this tussock has a finite width?
> logspline::poldlogspline(fit=myspline, q=0.01)
[1] 0.04138533
--
David Winsemius, MD
West Hartford, CT
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