MIMIC model : Expected covariance matrix is non-positive-definite.

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Joined: 07/31/2009 - 14:25
MIMIC model : Expected covariance matrix is non-positive-definite.

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)
sources   = manifests[1:3]

MIMIC <- mxModel("MIMIC", type="RAM",
manifestVars = manifests,
latentVars   = latents,
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) ),
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.
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Joined: 07/31/2009 - 15:24
Uh, what is mxStart?

Uh, what is mxStart?

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Joined: 02/04/2010 - 20:45
data definition

Shouldn't the data definition read something like this:

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))
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Joined: 07/31/2009 - 14:25
Thanks Andreas!

Thanks Andreas!
To help others, I put up a wiki page with a working version and a path diagram!

http://openmx.psyc.virginia.edu/wiki/example-models

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Joined: 02/04/2010 - 20:45
Great! I am sure that'll be

Great! I am sure that'll be very helpful to other users.

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Joined: 02/04/2010 - 20:45