Moderator in LGC

[constanze]

Hi everyone, 

I fitted a growth mixture model on my data across 15 time points. According to the fit indices a 3 class model seems to be the best way to go. Yet, only 2 of the 3 classes are of interest. Now I would like to add several predictors with class membership as a moderator (M; dummy coded).  Unfortunately, I can't really figure out how to implement the moderator. For now, I did it the following way, but I am pretty sure this is not correct (the code is presented in an condensed form )

base<- ' i =~ 1*TP_1 + .... + 1*TP_15
         s =~ 0*TP_1 + .... + 14*TP_15

#residual variance
TP_1~~r*TP_1
...
TP_15~~r*TP_15

#autocorrelated
TP_1~~s*TP_2
...
TP_14~~s*TP_15

# intercept & slope
i~ M*pred.1 + M*pred.2 + M*pred.3
s~ M*pred.1 + M*pred.2 + M*pred.3
'

I've been looking for answers on the group already, hope I haven't missed something, but it seems they deal with slightly different things, and I can't work out how to apply it to my own model.

Thanks you very much. 

[Terrence Jorgensen]

I would like to add several predictors with class membership as a moderator (M; dummy coded). 

lavaan ?model.syntax is not a ?formula object, for which asterisks are used very differently.  You need to include the lower-order effects, and specify a product term with the colon operator.

i~ M + pred.1 + pred.2 + pred.3 + M:pred.1 + M:pred.2 + M:pred.3

Terrence D. Jorgensen

Assistant Professor, Methods and Statistics

Research Institute for Child Development and Education, the University of Amsterdam

http://www.uva.nl/profile/t.d.jorgensen

 

[constanze]

Dear Terrence, 

thanks a lot for the speedy reply and the information. 

I fitted it accordingly, but it  seems there are problems with the predictor gender. 

                         Age          2   48 numeric   1    0  47.5416667 1.670195e+02    0     

18               Gender          3   48  factor      1    0          NA           NA    2  0|1

19             Duration          4   48 numeric   1    0 113.7916667 1.631349e+04    0     

20            class:Age     317   48 numeric   1    0  61.8333333 1.412652e+03     0     

21***      class:Gender  318    0 logical      1    0          NA           NA    0     

22       class:Duration    319   48 numeric  1    0 128.2916667 1.635310e+04    0     

Further, I do fit different so called "predictor families" to avoid the problem of multicollinearity. I am doing this, by including all predictors at once setting them at 0 (variance and covariance structure is already present). Then in several models I regress each predictor family solely on the intercept and the slope. 

Unfortunately, it seems that some predictor families show too little variance, or do I interpret the error message the wrong way? 

Error in chol.default(S) : 

  the leading minor of order 34 is not positive definite

In addition: Warning message:

In computeOmega(Sigma.hat = Sigma.hat, Mu.hat = Mu.hat, lavsamplestats = lavsamplestats,  :

  lav_model_gradient: Sigma.hat is not positive definite

Thanks again, and all the best, 

Constanze 

[constanze]

Hi again, 

thank you very much for the help concerning the moderator implementation. Unfortunately, I get a several different error messages. I went through older post in this group, and as far as I understood it, as long as lavaan has to handle an exogenous binary predictor/ moderator, such as gender or class membership in my case as well, one does not need to specifically specify this during model fit. (moderator and gender are numeric, defined by 0/1)

M_3 <- growth(m.3, data=data, missing = "fiml", estimator = "mlr",check.gradient = FALSE) 

Error in chol.default(S) :
  the leading minor of order 34 is not positive definite

In addition: There were 21 warnings (use warnings() to see them)
> use warnings(M_3)
Error: unexpected symbol in "use warnings"

I would really appreciate help both on how to specify the fit appropriately and avoid the error message. 

Thank you very much. 

All the best, 

Constanze 

[Patrick (Malone Quantitative)]

The error is from taking "use warnings" too literally!

Try a line with just

warnings()

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[Patrick (Malone Quantitative)]

Sorry, just the second error. But it still might help.

[constanze]

I am sinking into the ground, this is quiet embarrassing... Thank you nevertheless!!

Unfortunately, this is what I have to face now: 

1: In names(out)[1L] <- NAME :

  number of items to replace is not a multiple of replacement length Error in cat("1: In names(out)[1L] <- NAME :\n  number of items to replace is not a multiple of replacement length",  : 

  argument 2 (type 'S4') cannot be handled by 'cat'

Any thoughts? 

Thanks to every 1 or 2 cents on that concern. 

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NEW Service Models: http://malonequantitative.com

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