dose.p in MASS - R-help | R Mailing Lists

Tue, Jul 16, 2002 3:40 AM #

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:

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,
Albertus

Dr. Albertus J. Smit
Department of Botany
University of Cape Town
Private Bag Rondebosch
7700
South Africa
Tel. +27 21 689 3032
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Kenneth Cabrera

Tue, Jul 16, 2002 6:11 AM #

Hi R expert users:

I want to know if any body is working or have some functions
to apply times series disaggregation.

Thank you very much for your help

Kenneth

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Brian Ripley

Tue, Jul 16, 2002 6:48 AM #

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

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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John Fox

Tue, Jul 16, 2002 6:49 AM #

At 12:40 PM 7/16/2002 +0200, Smit, A, Albertus, Dr wrote:

Dear Albertus,

 From the help page for dose.p:

cf The terms in the coefficient vector giving the intercept and coefficient 
of (log-)dose

Apparently, your model (unlike the example on the help page) has only one 
predictor, presumably the log dose; there are, therefore, only two 
coefficients -- for the intercept and log dose.

I hope that this helps,
  John
-----------------------------------------------------
John Fox
Department of Sociology
McMaster University
Hamilton, Ontario, Canada L8S 4M4
email: jfox at mcmaster.ca
phone: 905-525-9140x23604
web: www.socsci.mcmaster.ca/jfox
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