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st: GLLAMM Help


From   Swati Agiwal <agiwa001@umn.edu>
To   statalist@hsphsun2.harvard.edu
Subject   st: GLLAMM Help
Date   Tue, 28 Aug 2007 15:24:02 CDT

Hello All,

I am using the GLLAMM program in Stata and wanted to know if anyone else is
using the same for fitting ordinal item response models.

I am fitting a simple one parameter as well as a two parameter item
response model. I am interpreting the random effect as the latent variable.
However, I am facing difficulties in introducing other explanatory
variables into the existing item response models. I have looked through the
GLLAMM manual and there arent any similar examples.

The current model I am fitting is :

g(P(y{i}{j}<s)) = k{s} - b{i} - n{j}...Model(1)

where g() is the ordinal probit function. y{i}{j} is the ordinal response
for person j on question/item i. k{s} are category thresholds, b{i} are
item biases and  n{j} are the person specific random intercepts, which I
interpret as the latent variables. Model(1) is easy to fit in GLLAMM.

To this i want to incorporate:

n{j}= a*w1{j}+ c*w2{j} + q{j}

That is, the latent variable n{j} is itself a function of person j specific
characteristics, say education w1{j} and income w2{j} and a new latent
variable q{j}. a and c are coefficients of the explanatory variables w1 and
w2.

Thus the final model that i want to fit is :

g(P(y{i}{j}<s)) = k{s} - b{i} - a*w1{j} - c*w2{j} - q{j}...Model(2)

I am using all the items and all the firms together is estimating this
model.
If any does have an idea as to how to fit Model(2) in GLLAMM please do let
me know.

Thanks in advance,
Swati 




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