I am conducting confirmatory factor analysis using lavaan in R with several both first- and second-order factors in the model (20 latent constructs and 97 items in total; n = 511; no missing values). After running the CFA, the model fit is not sufficient, but some low factor loadings, a couple Heywood cases and several indications from the modification index give some pointers for model improvement. Deleting some items from the model and re-structuring two factors based on an EFA eliminates Heywood cases and results in acceptable model fit (Chi-square=4117, DF=2646, CFI=.94, RMSEA=.038, SRMR=.052), however, the CFA of the adjusted model now returns the following error message: "covariance matrix of latent variables is not positive definite". There aren't any negative values in the covariance matrix though and also not in the correlation matrix.
I'm fairly new to this kind of statistical analysis and have no clue what causes this error and how to fix the issue. I'd appreciate any help. Please find attached the original and adjusted CFA measurement model as well as the covariance and correlation matrices of the adjusted model causing the NPD error.
Thanks a lot for your input!
The error says that your cor matrix is not satisfactory for the command you issue no neg or 0 values are allowed. All entries must be gt 0 LTE to 1. If that's not the case in your
data set fix it. If otherwise ask again and include code. Best wishes David Booth
PS this problem is best dealt with using a cor matrix and not a cov matrix because the conditions are easier to see.
How did you decide your sample size with 20 latent variables and 97 items? How many parameters are you estimating? Your sample size seems small for this.
Sometimes a message like this occurs when several factors are highly (but not necessarily perfectly or > |1|) correlated. High correlations among factors can cause linear dependencies (e.g., one factor being perfectly predictable from a set of other factors) without there being negative variance estimates or correlation estimates > |1|.
- Badges
- Science method
- Similar topics
- Mathematics
- Statistics
- Statistical Techniques
- Structural Equation Modeling