[R] Breakpoint in logistic GLM with 'segmented' package - error: replacement length zero

[Vito Muggeo (UniPa)]

dear Peter,
Your code appears correct, so it is difficult to reply without the data..

If you are interested in further details, please contact me off-list

vito


Il 25/05/2012 15.34, Peter Hoitinga ha scritto:
> Hello all,
>
> I've been having trouble with assessing a breakpoint in a logistic GLM
> with two explanatory variables. For this analysis I've been using the
> 'segmented' package version 0.2-9.1. But I keep getting an error and I
> don't see where I would be going awry. The situation is the following:
>
> Two explanatory variables:
> bedekking - a variable with possible values between 0 and 1 - mine
> runs from 0.05 to 0.5, increasing with steps of 0.05
> s.size - a count variable - increases from 3 to 25 with steps of 1,
> and from 25 to 60 with steps of 5
>
> Each combination of s.size and bedekking has 100 repeats so the
> resulting dataframe 'dat.al2' consists of 30000 observations of 3
> variables.
>
> Because the response variable has values between 0 and 1, I used a logistic GLM:
>
>> gmodel<- glm(R.AUC ~ bedekking + s.size, data=dat.al2, family = quasibinomial(link=logit))
>
> R.AUC increases with increasing s.size and decreasing bedekking,
> looking at the graph shows that the association reaches a plateau at a
> s.size of 10 and a bedekking of 0.45. So these are the values I use in
> 'psi' argument in the 'segmented' function
>
>> psi.mod<- list(0.45, 10)
>> names(psi.mod)<- c("bedekking", "s.size")
>
> Then I attempt to run the 'segmented' function:
>
>> seg.gm<- segmented(obj = gmodel, seg.Z= ~bedekking + s.size, psi = psi.mod)
>
> When I run this, after half a minute I get the following error:
>
> Error in ifelse(is.list(o0), o0$dev.no.gap, 10^12) :
>    replacement has length zero
>
> Does anybody know what might be causing this error, and could somebody
> point out where I might go wrong?
>
> Thanks in advance,
>
> Peter
>
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-- 
====================================
Vito M.R. Muggeo
Dip.to Sc Statist e Matem `Vianelli'
Università di Palermo
viale delle Scienze, edificio 13
90128 Palermo - ITALY
tel: 091 23895240
fax: 091 485726
http://dssm.unipa.it/vmuggeo