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

From: Rizwan Younis <rizwanyounis_at_hotmail.com>
Date: Mon, 16 Jul 2007 17:27:28 -0400


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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