Dear S-news maling list
members,
I need to model the amount of chlorophyll-a in
Portuguese waters as a function of the upwelling pulses felt in the previous
days to the day when water samples were collected, water stratification and
temperature at the surface of the ocean. As chlorophyll-a cannot take
negative values, I thought that it would be a good idea to fit a Gaussian
truncated regression model at the point zero. To attain this goal I've used the
"censorReg" function in SPLUS 6.0, namely:
adjustment<-censorReg(censor(dados.fito$clorophyll)
~
dados.fito$Stratification+dados.fito$Temperature+dados.fito$upwell0days+dados.fito$upwell1day+dados.fito$upwell2days+dados.fito$upwell3days+
dados.fito$upwell4days+dados.fito$upwell5days+dados.fito$upwell6days+dados.fito$upwell7days,
data="">
Unfortunately, this function did not work properly with
my data set because I got a few warning messages:
1: problems
in covariance matrix computations; error code iervcv = 1 in: censorReg.mlest(Yi,
censor.codesi, Xi, casewti, distribution,
link,
parameter.fixed =
parameter.fixed, fixed = fixed, control = ....
2: Maximum change in parameter does not change the likelihood
in: censorReg.mlest(Yi, censor.codesi, NULL, casewti, distribution, link,
parameter.fixed = parms.fixed, fixed = fix2p, control = control,
....
3: Information matrix is not positive definite in:
censorReg.mlest(Yi, censor.codesi, NULL, casewti, distribution, link, parameter.fixed = parms.fixed, fixed = fix2p,
control = control, ....
Has anybody experience with such warnings? I don't know
what is the effect of such pitfalls in the estimated
parameters.
I would also like to ask if anyone has ever tried to
run a stepwise function afterwards? The reason I'm asking for this is because
I would like to run a stepwise function (or a
similiar one) to select a statistical significant subset of those variables.
I've already tried the functions step, step.glm but neither of
them worked properly. I get the following message:
problems in names(z) <- names(wz)
<- yn: supplied 207 names for a vector of lenght 414. Use traceback() to see
the call stack in: remove(list).
Warning massages: Problem:
internal error: trying to set internal exit action in frame , must be between 1
and 0.
After writing the command "traceback()" in the
command prompt, the SPLUS program aborts!
Has anybody ever had similar problems? Can anyone
provide some hints on how to get through this matter?
Thanks in advanced.
Best regards,
Helena
Mouriño.