[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]
st: Some questions on IRT using GLLAMM
Prathiba Natesan wrote:
I have been working on GLLAMM for some research projects . I find
the program very handy and useful particularly when it comes to Item
However, I have some specific questions about applying GLLAMM to IRT. I
would appreciate it if someone could get back to me with answers to
these questions. I am trying to estimate the difficulty, discrimination
and threshold values for a polytomous dataset. I have run the gllamm
with item specific thresholds and now have the parameters. I need some
assistance in identifying the parameters. I have _cut11 for d2-d6 and
cons,..., _cut14 for d2-d6 and cons and the level 2 coefficients for
random effect 1. Here are my specific questions:
1. There should be only 3 thresholds (for 4 categories). So how do I
tell which of the parameters are the threshold, difficulty and
2. I constrained the standard deviation of the latent variable using the
constraint "def 1 [id1_1]d1=1" syntax and then estimated the oprobit
model again with the constraint and the frload option. Are the level 2
coefficients I have now, the discrimination parameters?
On a different note:
1. For a polytomous dataset, what causes the estimates to not converge?
Can something be done about it? Does it say something about the data?
2. When the program says, flat or discontinuous region encountered, I
understand that there is trouble in evaluating the integral due to this.
But why does this happen? Or rather, what do we do in such situations?
3. This is a very basic question. When I have certain factors (from the
factor analysis), should I perform GLLAMM for each factor (GLLAMM on
items belonging to this factor) individually? I am doing this because I
think that it would be
easier to tackle unidimensional models than multidimensional models.
Will there be any problems in doing this (I am thinking analogous to
performing many ANOVAs instead of one MANOVA which inflates the type-I
Any advice would be of great help. Thanks
* For searches and help try: