I am trying to run a mediation model examining country group differences in impression management. I am having some difficulty diagnosing the problem in my lavaan model.

I have three groups: country A (n = 300), country B (n = 325), and country C (n = 320), which are dummy coded into variables A and B.

I specified my mediation model as follows:

`model<- '#Imp Mgmt Styles Factor sprom =~ IM_Sup08+IM_Pr28+IM_Sup27+IM_Pr08+IM_Pr28+IM_Pr27+IM_Sub08+IM_Sub28+IM_Sub27 ingrt =~ IM_Sup14+IM_Sup15+IM_Sup19+IM_Pr14+IM_Pr15+IM_Pr19+IM_Sub14+IM_Sub15+IM_Sub19 exemp =~ IM_Sup06+IM_Sup07+IM_Sup29+IM_Pr06+IM_Pr07+IM_Pr29+IM_Sub06+IM_Sub07+IM_Sub29 #Target Factor super =~ IM_Sup08+IM_Sup28+IM_Sup27+IM_Sup14+IM_Sup15+IM_Sup19+IM_Sup06+IM_Sup07+IM_Sup29 peer =~ IM_Pr08+IM_Pr28+IM_Pr27+IM_Pr14+IM_Pr15+IM_Pr19+IM_Pr06+IM_Pr07+IM_Pr29 sub =~ IM_Sub08+IM_Sub28+IM_Sub27+IM_Sub14+IM_Sub15+IM_Sub19+IM_Sub06+IM_Sub07+IM_Sub29 #Predictors sprom ~ TrnvPssb ingrt ~ TrnvPssb exemp ~ TrnvPssb super ~ TrnvPssb peer ~ TrnvPssb sub ~ TrnvPssb TrnvPssb ~ A + B' fit<-cfa(model = model, std.lv = TRUE, data = dt, estimator = "WLSMV") `

When I attempt to run it, I get the error `lavaan ERROR: sample covariance matrix is not positive-definite`

. I have dismantled and tested every other part of the model so I know that the problem is not with the other parts of the model. In fact, I can run it with just one of the dummy-coded variables (A or B) and it works perfectly.

I wonder if it is a shared variance issue with the grouping variable. How would I be able to test this and fix it?

Thank you for sharing your knowledge and expertise.

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#### Best Answer

This is a general SEM problem, not a lavaan problem.

Something has gone wrong with your sample covariance matrix. It's hard to know what, but you can tell by looking at it. It shouldn't matter what your model looks like, this error is about your data.

Use:

`[email protected]@cov `

If it's not clear from that, paste the output and come back.

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