Ah, the larger problem is in how you specify your model. You provide
no parameter names, nor starting estimates (even an NA). See the sem
help file for an example. Basically, it must look something like as
follows
model <- specify.model()
Z -> M, zm, NA
Z -> I, zi, NA
etc.
On Jul 20, 2009, at 11:37 PM, Stein, Luba (AIM SE) wrote:
Hi,
[,1] [,2] [,3]
[1,] 4.820719e-03 -5.558801e-05 -5.718939e-05
[2,] -5.558801e-05 4.763194e-06 -7.661872e-06
[3,] -5.718939e-05 -7.661872e-06 1.662150e-03
This is mod.cov. It is the covariance matrix of (R, I, M).
R, I and M are vectors of length 109 which are contained in the file
data4.csv.
As far as I understood the package sem. I consider R, I and M as the
external veriables and Z as the latent variable which I will receive
as an result after calculating the estimated errors and parameters.
This is what atually is missing in the output.
Moreover, the output provides the information about the quality of
the fitted model. I have to admit that this model does not fit quite
well.
Nevertheless, it should provide the estimated errors like it does
just for the first variable Z ->M.
Thanks a lot for your help,
Luba
-----Urspr?ngliche Nachricht-----
Von: r-help-boun...@r-project.org [mailto:r-help-boun...@r-
project.org] Im Auftrag von Jarrett Byrnes
Gesendet: Dienstag, 21. Juli 2009 08:19
An: Stein, Luba (AIM SE)
Cc: r-help@r-project.org
Betreff: Re: [R] Another SEM question
You don't appear to be defining Z here.
Might that be the problem?
Or, I, M, and R may not be defined either. It is unclear. What does
mod.cov look like?
On Jul 20, 2009, at 11:11 PM, Stein, Luba (AIM SE) wrote:
Thank you for your advice. So I am sending the whole code
data.dir <- file.path(home.dir, "Data")
file <- file.path(data.dir, "data4.csv")
SEM <- read.csv(file)
print(SEM)
library(sem)
SEM1 <- as.matrix(cbind(SEM$R1, SEM$I1, SEM$M1))
print(SEM1)
mod.cov <- cov(SEM1)
print(mod.cov)
I <- SEM$I1
M <- SEM$M1
R <- SEM$R1
model <- specify.model()
Z -> M
Z -> I
Z -> R
M <-> M
I <-> I
R <-> R
Z <-> Z
sem.mod <- sem(model, mod.cov, N=109)
summary(sem.mod)
All vectors have a length of 109.
Thank you for your help once again.
Best wishes,
Luba
-----Urspr?ngliche Nachricht-----
Von: r-help-boun...@r-project.org [mailto:r-help-boun...@r-
project.org] Im Auftrag von Jarrett Byrnes
Gesendet: Montag, 20. Juli 2009 18:25
An: Stein, Luba (AIM SE)
Cc: r-help@r-project.org
Betreff: Re: [R] Another SEM question
Luba,
If you could provide the code you ran, perhaps the listserv can be of
help.
On Jul 20, 2009, at 7:55 AM, Stein, Luba (AIM SE) wrote:
Hello,
I use the function sem the following way
sem.mod <- sem(model, mod.cov, N=109) where the variables are
modelled:
Z -> M
Z -> I
Z -> R
M <-> M
I <-> I
R <-> R
Z <-> Z
The output is
...
Normalized Residuals
Min. 1st Qu. Median Mean 3rd Qu. Max.
-7.3300 -0.2750 -0.2670 -0.1290 -0.0369 9.0300
Parameter Estimates
Estimate Std Error z value Pr(>|z|)
0.0021625 0.00017037 12.693 0 M <--- Z
Iterations = 13
In "Structural Equation Modeling With the sem Package in R" by John
Fox is stated that there should be an output for each external
variable.
Where is my fault, that I receive the output only for the first
variable?
Thanks for your help,
Luba
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and provide commented, minimal, self-contained, reproducible code.
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