[R] dose.p in MASS

Smit, A, Albertus, Dr ajsmit at botzoo.uct.ac.za
Tue Jul 16 12:40:47 CEST 2002

Dear all

I need to obtain an estimate of the 50% lethal dose (LD50) from a 
logistic regression model obtained by applying the glm procedure to 
some binomial data. The model appears to fit the data very well. I 
used dope.p from MASS to try and find LD50.

The following output appears:

> dose.p(iso.glm.logit, cf = c(1,3), p = 1:3/4)
Error in dose.p(iso.glm.logit, cf = c(1, 3), p = 1:3/4) : 
        subscript out of bounds

What is the problem here? The error disappears when fiddle around 
with cf (e.g., cf = c(1,2)), but I have no idea what this does, or even 
what the cf parameter is used for.

Any help appreciated.

Kind regards,

Dr. Albertus J. Smit
Department of Botany
University of Cape Town
Private Bag Rondebosch
South Africa
Tel. +27 21 689 3032
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