[Rd] Error while fitting Partial Proportional Odds model using vglm

[Prof Brian Ripley]

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On Mon, 16 Jul 2007, Rizwan Younis wrote:

> Dear R developers:
>
> I am trying to fit a PPO model using vglm from the library VGAM, and get an
> error while executing the code. Here is the data, code, and error:
>
> Data: first row is the column names. a = age, and 1,2,3, 4 and 5 are
> condition grades.
>
>  a  1 2 3  4 5
>  1  1 0 0  0 0
>  2 84 2 7 10 2
>  3 16 0 6  6 2
>  4 13 0 3  4 0
>  5  0 0 0  1 0
>
> Library(VGAM)
>
> rc13<-read.table("icg_rcPivot_group2.txt",header=F)
> names(rc13)<-c("a","1","2","3","4","5")
>
> ppo<-vglm(cbind(rc13[,2],rc13[,3],rc13[,4],rc13[,5],rc13[,6])~a,family =
> cumulative(link = logit, parallel = F , reverse = F),na.action=na.pass,
> data=rc13)
> summary(ppo)
>
> I get the following error:
>
> Error in "[<-"(`*tmp*`, , index, value = c(1.13512932539841,
> 0.533057528200189,  :
> 	number of items to replace is not a multiple of replacement length
> In addition: Warning messages:
> 1: NaNs produced in: log(x)
> 2: fitted values close to 0 or 1 in: tfun(mu = mu, y = y, w = w, res =
> FALSE, eta = eta, extra)
> 3: 19 elements replaced by 1.819e-12 in: checkwz(wz, M = M, trace = trace,
> wzeps = control$wzepsilon)
>
>
> Ironically, it works ok with Proportional Odds (change parallel = T above),
> but fails with PPO (parallel = F).
>
> I will appreciate any help to fix this problem.
> Thanks
>
> Rizwan Younis
> Grad Student
> University of Waterloo
> Waterloo, ON Canada
>
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>

-- 
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)
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