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


Terry Beutel

Agri-Science Queensland

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