[R] dose.p in MASS

[ripley@stats.ox.ac.uk]

On Tue, 16 Jul 2002, Smit, A, Albertus, Dr wrote:

> 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.

There is a help page for dose.p(), and it does explain the argument `cf'!
Probably the default cf=1:2 is what you want, but without seeing how you
created iso.glm.logit we can only guess.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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