HELP WITH LAVAAN ERROR. Error with path analysis using latent variable

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Lindy Howe

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Jan 2, 2020, 2:07:53 PM1/2/20
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Hi all  - I am completing a mediation analysis using lavaan. The analysis has 2 causal factors (TAI and mBDI), 1 mediator (BPD), and 1 DV (SUD) which is a latent variable. 

I am attempting to run this model using lavaan, but am getting an error when fitting that I cant fix!! Any help? Syntax below. 

> model <- '  SUD.sum =~ Alc.Sum+Drug.Sum+MJ.Sum    
+             BPD.Sum ~ TAI.SUM + mBDIII.SUM
+             SUD.sum ~ BPD.Sum + TAI.SUM + mBDIII.SUM
+             mBDIII.SUM ~~ mBDIII.SUM
+             TAI.SUM ~~ TAI.SUM
+             mBDIII.SUM ~~ TAI.SUM
+             BPD.Sum ~~ BPD.Sum
+             SUD.sum ~~ SUD.sum'
> fit <- lavaan(model, estimator = 'MLF', data=df)
Error in lav_model_estimate(lavmodel = lavmodel, lavpartable = lavpartable,  : 
  lavaan ERROR: initial model-implied matrix (Sigma) is not positive definite;
  check your model and/or starting parameters.

Note: The error goes away when I remove the latent variable, but I need the latent variable to be included. 

Thanks!

Terrence Jorgensen

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Jan 3, 2020, 11:16:43 AM1/3/20
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I am attempting to run this model using lavaan

Try using sem() instead, which automatically adds the residual-variance estimates you have omitted from your syntax (the cause of your error).

I hope your N is large enough for MLF.  First-order information does not perform well with modest sample sizes.

Terrence D. Jorgensen
Assistant Professor, Methods and Statistics
Research Institute for Child Development and Education, the University of Amsterdam

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