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Messages - navid

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Questions and Answers / Re: contrasting results in ConQuest
« on: December 13, 2013, 01:56:50 PM »
Thank you Eveline,
I will try the options.
With respect to your last comment: "I am not sure what you mean with an overall ability. If you run a multi-dimensional model, students receive an ability estimate for each dimension.". Yes, I know a separate ability estimate is reported for each dimension but I read some papers where the ability estimates across models with different dimensionality design (testlets vs multidimensional ones) were compared. They couldn't have done the comparison for each separate dimension because the number of dimensions is not the same across models.
I once asked a well-known figure in Rasch modelling how we can get an overall ability estimate in multidimensional MRCMLM. He said "simply add the individual ability estimates on each dimension"! This doesn't make much sense to me because the ability estimates are not on the same scale. I thought there may be a more plausible option.

Questions and Answers / Re: contrasting results in ConQuest
« on: December 09, 2013, 12:44:31 PM »
Sorry I guess my post has been a bit vague.
We want to compare the relative fits of these models. Each time I run the ConQuest, I get a different deviance! Hence, sometimes the within-dimensional model has better fit but if I run the analyses again, because I get a different deviance and hence AIC and BIC indices, the testlet model may show better fit. That is, the estimates are not stable. Should I increase the number of nodes? How many nodes will be needed for stable estimation?

A related question is how should we compare the ability estimates across the models? Because ConQuest doesn't offer an overal ability estimate for examinees, how should I compare the ability estimates in between-item multidimensional model and those obtained in testlet?

Hope it makes sense this time!

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 / Re: Fit indices in ConQuest
« on: December 06, 2013, 03:41:19 PM »
Thank you George for your response.
As for the third question, we are fitting a testlet model which I assume falls within the category of within-item multidimensional models. Doesn't it? Can we still use the difference between deviances to compare relative fit?


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 / Re: a problem with the thresholds map
« on: November 15, 2013, 12:03:07 AM »
I just sent you the controle and data files.


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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