Hello, I have got a question about the thresholds in SEM of ordinal variables and really need your help.
1) I found tow kinds of scripts of saturate SEM of one ordinal variable, one script constrains the free status of thresholds, and another one does not. I can't figure out which one to follow.
the first one: [6]
nth <- 3 frTh <- matrix(rep(c(F,F,(rep(T,nth-2)))),nrow=nth,ncol=nv) # free status for thresholds thinMZ <- mxMatrix( type="Full", nrow=nth, ncol=ntv, free=frTh, values=svTh, lbound=lbTh, labels=labThMZ, name="thinMZ" )
the second one: [7]
nth <- 3 thinMZ <- mxMatrix( type="Full", nrow=nth, ncol=ntv, free=TRUE, values=svTh, lbound=lbTh, labels=labThMZ, name="thinMZ" )
2)
If I do need to constrain the free status of thresholds, then how many thresholds should I fix?
In the first script, the number of thresholds is 3 and two shresholds are fixed. If my ordinal variable is categorized into 5 groups, and then the number of thresholds should be 4, then how many thresholds should I fix? three or two? In fact, I don't konw the reason for fixing thresholds. So, please don't mind my kind of stupid question.
I would be really appreciated for your reply!
Thanks!