Hi all,
Any clues on getting this mimic model working? I've explored a range of start-vals... always getting NonPosDef
omx seems not to like models with formative structures (i've got it going with the formative measures having residual variance, rather than being correlated)
Example is from chapter 13 Schumacker and Lomax Beginner's guide to SEM
data <- data.frame(matrix(c( 1.000, 0.304, 0.305, 0.100, 0.284, 0.176, 0.304, 1.000, 0.344, 0.156, 0.192, 0.136, 0.305, 0.344, 1.000, 0.158, 0.324, 0.226, 0.100, 0.156, 0.158, 1.000, 0.360, 0.210, 0.284, 0.192, 0.324, 0.360, 1.000, 0.265, 0.176, 0.136, 0.226, 0.210, 0.265, 1.000 ),nrow=6)) manifests = c("income", "occup", "educ", "church", "member", "friends") dimnames(data) = list(manifests, manifests) latents = "social" # 1 latent, with three formative inputs, and three reflective outputs (each with residuals) receivers = manifests[4:6] sources = manifests[1:3] MIMIC <- mxModel("MIMIC", type="RAM", manifestVars = manifests, latentVars = latents, # Factor loadings mxPath(from = sources , to = "social" , values = c(.23, .11, .3) ), mxPath(from = "social", to = receivers, values = c(.47, .74,.4) ), # Correlated sources mxPath(from = sources, connect = "unique.bivariate", arrows = 2, values = c(.3,.2,.3) ), # Residual variance on receivers mxPath(from = receivers, arrows = 2, values = c(.32,.31,.28) ), mxData(data, type = "cov", numObs = 530) ) MIMIC= mxRun(MIMIC); summary(MIMIC) Error: The job for model 'MIMIC' exited abnormally with the error message: Expected covariance matrix is non-positive-definite.