[R] tree mortality risk model using glm()

[Tord Snall]

Dear all,

I've used glm(family=binomial(link="logit")) several times, but now I think
that a log link is more appropriate. 

I want to fit a model for probability of tree fall (TF)), with tree
diameter (dbh) and soil moisure (soil) as predictors. A large number of
trees have been checked every second year whether they stand up (0) or have
fallen (1).

I assume that the tree fall probability is predicted by

TF = 1 - exp(-(dbh + soil))
log(1 - TF) = -(dbh + soil)

I thought the following call would fit the model, but I get an error message.
test<- glm(1-TF ~ dbh +soil , data = extdat, family = quasibinomial(link =
"log"))
Error: no valid set of coefficients has been found:please supply starting
values
In addition: Warning message: 
NaNs produced in: log(x) 

Could someone give a clue on what is wrong. Is there another way to fit
this model? 

People have asked about exponential models before but they have dealt with
continuous responses.


Thanks in advance!

Yours sincerely,
Tord



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Tord Snäll
Avd. f växtekologi, Evolutionsbiologiskt centrum, Uppsala universitet
Dept. of Plant Ecology, Evolutionary Biology Centre, Uppsala University
Villavägen 14			
SE-752 36 Uppsala, Sweden
Tel: 018-471 28 82 (int +46 18 471 28 82) (work)
Tel: 018-25 71 33 (int +46 18 25 71 33) (home)
Fax: 018-55 34 19 (int +46 18 55 34 19) (work)
E-mail: Tord.Snall at ebc.uu.se
Check this: http://www.vaxtbio.uu.se/resfold/snall.htm!