Equal threshold intervals in SEM with categorical variables

Skip to first unread message

tran viet Yen

Feb 21, 2019, 3:09:05 AM2/21/19
to lavaan
Dear all,

When estimating a SEM with categorical variables using, can we constrain the intervals between thresholds? For instance in this simple model with the latent variable A and two indicator A1 and A2:

A =~ A1 + A2
A1 | a1*t1 + a2*t2 + a3*t3 + a4*t4
A2 | a1*t1 + a2*t2 + a3*t3 + a4*t4

The problem is, if I want to place some constraints on the thresholds, for instance to force a2 = -a3 and (a2-a1) = (a4-a3) like in this picture:


then how we will modify the code to obtain this?

Thank you so much for reading this topic.


Tran Viet Yen.

Terrence Jorgensen

Feb 21, 2019, 4:04:10 PM2/21/19
to lavaan
how we will modify the code to obtain this?

You can literally put those in your model syntax, using the "==" operator to define any (in)equality constraint(s) on labeled parameters.  But you need to express the left-hand side as a single parameter, which can be user-defined.

model <- '

A =~ A1 + A2
A1 | a1*t1 + a2*t2 + a3*t3 + a4*t4
A2 | a1*t1 + a2*t2 + a3*t3 + a4*t4

a2 == -1*a3

diff21 := a2 - a1
diff43 := a4 - a3
diff21 == diff43

Terrence D. Jorgensen
Assistant Professor, Methods and Statistics
Research Institute for Child Development and Education, the University of Amsterdam

tran viet Yen

Feb 22, 2019, 1:25:05 AM2/22/19
to lav...@googlegroups.com
Dear Terrece,

Thank you very much for the instructions. This is exactly what I'm looking for. You have explained it in a very detailed manner.

Best regards,

Tran Viet Yen.

You received this message because you are subscribed to the Google Groups "lavaan" group.
To unsubscribe from this group and stop receiving emails from it, send an email to lavaan+un...@googlegroups.com.
To post to this group, send email to lav...@googlegroups.com.
Visit this group at https://groups.google.com/group/lavaan.
For more options, visit https://groups.google.com/d/optout.

Trần Việt Yên
PhD Student
Civil and Environmental Engineering Department, Graduate school of Engineering, Nagoya University, Japan.
Reply all
Reply to author
0 new messages