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Context: I'm trying to analyse some data where I have four explanatory variables named "Estimulo", "Barra", "DPI" and "Viendocon" (all of them are taken as factors) and one response variable, named "Vueltasmin", which is a numeric one.

As the explanatory variables are measured repeatedly (but not in a time-dependant manner, like in a repeated measures design) I chose a gls model. This gls strategy was selected after trying an lmer model, where I rejected Shapiro-Wilk's test for normality and had some conic-like pattern in a QQplot.

I try to modelate the variance using different strategies: VarFixed, VarIdent,Varpower and VarExp. Now here is where I can't go on: there is some error I'm getting that I'm not understanding what does it means.

For example, I run: m2a<-gls(Vueltasmin~DPI * Barra * Estimulo * Viendocon,weights=varFixed(~Barra),data=Datos)

and getting: Error in glsEstimate(object, control = control) : computed "gls" fit is singular, rank 18.

When I try to run a VarIdent, I run: m3<-gls(Vueltasmin~DPIBarraEstimulo*Viendocon, weights=varIdent(form=~1|Barra), data=Datos)

and get the same.

I leave the following link where you can find the script (named "Script tesis lic") and the data base I'm using (named "EXP1"):

http://dropcanvas.com/hy6ds

If anyone could help or orient me, I would be very grateful.

Thank you very much in advance,

Yair.

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  • $\begingroup$ Please add a reproducible example for people to work with. $\endgroup$ – gung - Reinstate Monica Feb 6 '17 at 1:28
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    $\begingroup$ I'm voting to close this question as off-topic because it is about how to use R without a reproducible example. $\endgroup$ – gung - Reinstate Monica Feb 6 '17 at 1:28
  • $\begingroup$ I'm sorry for not doing it at first, I have added my data base and R-script inn my question. Thanks for noticing! $\endgroup$ – ybarnatan Feb 6 '17 at 17:24
  • $\begingroup$ Links tend to go dead & the goal of the SE system is to create a permanent repository of high quality information about (say) statistics in the form of questions & answers. Please include a small reproducible example in the post. $\endgroup$ – gung - Reinstate Monica Feb 6 '17 at 17:28
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Since your data is about the repeated measurement, I suggest you to take the "nlme" or "lmer" package to analyze your data. for example,

m2a <- lme(Vueltasmin ~ DPI * Barra * Estimulo * Viendocon, random = ~1|Subject, data=Datos, na.action = na.omit, method = "REML")

Hope this is helpful to you!

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  • $\begingroup$ Pcrainy Huang, first of all, thank you for your answer. Secondly, I tried your suggestion, but got another error message: "Error in MEEM(object, conLin, control$niterEM) : Singularity in backsolve at level 0, block 1 " So I'm not sure I got it yet. I added the script and the data base I'm using in case you might find my mistake inthere. Thanks a lot again! $\endgroup$ – ybarnatan Feb 6 '17 at 17:23

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