[R] System of logistics Equations

[Bernardo Rangel Tura]

Hi R-masters

I need yours help about a problema in one of may ongoing researchers.

In my research the subjects (20 in total) answer 60 questions (20 type
G, 20 type S and 20 type P).

Which questions is classified about 3 factor (2 level each) and the
subject score with 2 scale (not integer value is possible but rare): Val
range -7 to 7 and other Car range 1 to 7.

This a code to fake database of research 

Subj<-rep(1:20,each=60)
Sti<-rep(c("G","S","P"),40)
SP<-rep(c("S","P"),60)
AG<-rep(c("A","P"),60)
Mer<-rep(c("M","NM"),60)
Car<-round(runif(120,1,7),0)
Val<-round(runif(120,-7,7),0)
base<-data.frame(Subj,Sti,SP,AG,Mer,Car,Val)

In my hypothesis:

logit(Sti=="G") ~ SP+AG+Mer+Car+Val+SP*Car+Mer*Val+AG*Val + errorG

logit(Sti=="S") ~ SP+AG+Mer+Car+Val+SP*Car+Mer*Val+AG*Val + errorS

logit(Sti=="P") ~ SP+AG+Mer+Car+Val+SP*Car+Mer*Val+AG*Val + errorP

I test and the 3 terms of error (errorG,errorS,errorP) is correlated.

So I think useful adjust a system of logistic equations to tread the 3
equations and in same time to obtain estimatives of effects and
uncorrelated error terms.


The systemfit package fit linear system and non-linear system but is
possible adjust a logistic system in R?

Thanks in advance



-- 
Bernardo Rangel Tura, M.D,MPH,Ph.D
National Institute of Cardiology
Brazil