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Questions and Answers / contrasting results in ConQuest
« on: December 06, 2013, 08:23:47 PM »
As a follow-up to my previous post, we are doing a MRCMLM analysis using the ConQuest. The test has 70 items and six subtests. We have to test eight models and see which one has better fit: a unidimensional model, two between-item multidimensional models (with 5 and 6 dimensions), and five testlet models. The problem is that we get drastically different results each time we do the analysis. I know this may be partly due to the iteration that ConQuest goes through but what should we do?
Any advice is appreciated.


Questions and Answers / Fit indices in ConQuest
« on: November 29, 2013, 10:49:10 AM »
We are doing a ConQuest analysis of a language proficiency test. We intend
to compare four models: a unidimensiona Rasch model, an MRCMLM with 6
factors and between-item multidimensionality, an MRCMLM with 5 factors and
between-item multidimensionality, and a testlet model (with one general
dimension and six specific factors). We want to compare the relative fits
of the models. I have a couple of questions and would be grateful to
receive an explanation from you.

1. Is the deviance statistic reported in ConQuest equal to the -2 Log
Likelihood statistic? Is it the same as G2 reported in Rasch papers?

2. How is the AIC and BIC statistics computed from deviance? (I know these can be estimated from chi-square but is an overall chi-square reported in ConQuest?)
3. Can we consider the testlet model to also have a hierarchical relation
to other models in our study? (so that we can compare their relative fit using the difference in their deviance indices).

Many thanks in advance.


Questions and Answers / a problem with the thresholds map
« on: November 11, 2013, 10:45:25 AM »
I'm doing a ConQuest analysis of a multidimensional likert scale. The syntax I have written is:

datafile tses.sav! filetype=spss, responses=V1 to V24;
codes 1,2,3,4,5;
score (1,2,3,4,5) (0,1,2,3,4) () () !items (1,2,4,6,9,12,14,22);
score (1,2,3,4,5) () (0,1,2,3,4) () !items (7,10,11,17,18,20,23,24);
score (1,2,3,4,5) () () (0,1,2,3,4) !items (3,5,8,13,15,16,19,21);
model item + Step;
show ! estimates=latent >> tses.shw;
itanal >> tses.itn;

The prolem I have is with the output. I want the item-person map which also shows the thresholds. However, the output table I receive does not show that. I have attached the output.
Many thanks for any advice.


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