Messages

1

Questions and Answers / ConQuest Output Question

« on: April 03, 2017, 06:39:20 AM »

Dear All,
In ConQuest output under the variance/covariance matrix you can find the variance for each dimension. Next to each variance between parentheses there is another value. What is that value? The manual doesn’t say anything about it.
Thanks
Georg II

CONDITIONAL COVARIANCE/CORRELATION MATRIX

                                                               Dimension
                         ------------------------------------------------------------------------------------------
Dimension                    1                 2                 3                 4                 5

Dimension_1                                  0.000*            0.000*            0.000*            0.000*         
Dimension_2                0.000*                              0.000*            0.000*            0.000*         
Dimension_3                0.000*            0.000*                              0.000*            0.000*         
Dimension_4                0.000*            0.000*            0.000*                              0.000*         
Dimension_5                0.000*            0.000*            0.000*            0.000*                           
-------------------------------------------------------------------------------------------------------------------
Variance                   0.182  ( 0.009)   0.240  ( 0.012)   0.401  ( 0.020)   0.273  ( 0.013)   1.523  ( 0.074)
-------------------------------------------------------------------------------------------------------------------

2

Questions and Answers / Different item estimates across models?

« on: January 17, 2017, 05:42:54 PM »

Dear colleagues,

I’d be thankful if you replied this question.
I separately fitted two models to a data set: a unidimensional and a within-item two dimensional model. The item difficulty estimates of the items which simultaneously load on a second dimension in the two-dimensional model differ noticeably from the values they have in the unidimensional model. The items which load on only one dimension have the same estimates across the two analyses. What does this mean?
Thanks for your help

3

Questions and Answers / Re: Multidimensionality & reliability

« on: February 12, 2014, 04:39:56 PM »

Thank you Eveline,
I tried the command "keeplastests=yes". It looks like:

model item + step;
Estimate ! nodes=3000, method=montecarlo, Keeplastest=yes;
show !estimate=latent >> run1.shw;
itanal >> run1.itn;

But it gives this error message: "Unknown command or argument: ‘keeplastest’"
Maybe I haven't written it in the right place?

Georg II

4

Questions and Answers / Re: Multidimensionality & reliability

« on: January 28, 2014, 02:02:01 PM »

Hi Eveline,
I got this message when the 5-dimensioanl analysis converged:
"Convergence has occurred but a solution with a higher likelihood was encountered at iteration 148 The results for this earlier solution will be retained. Rerunning this analysis using current estimates as initial values and/or increasing the number of nodes is strongly advised".

The number of nodes was 1000. I reran the 5-dimensioanl analysis with 3000 nodes. It gives the same message at the end. This analysis has a better fit than the unidimensional analysis and the reliabilities are smaller (than the one with 1000 nodes) but still greater than the reliability of the single dimension with 25 items.
Do you think I should increase the number of nodes?


The show file for 1-dimensioanl model says "Iterations terminated because the convergence criteria were reached."
The other strange thing about this analysis is that this is the first time I see a unidimensional model fits better than a multidimensional model (when nodes=1000)!

Thanks
Georg II

5

Questions and Answers / Multidimensionality & reliability

« on: January 26, 2014, 09:43:46 AM »

I have a scale with 25 items. I fitted a unidimensional model and a 5-dimensional model.
The unidimensional model fits significantly better. The correlations between dimensions are above .95 in the multidimensional model.
The strange thing is that EAP reliability of the unidimensional scale with 25 items is .82 while the EAP reliabilities of the subscales, each having only five items, are above .92. I could understand it if the multidimensional model had a better fit. Because then one could argue that forcing irrelevant items which belong to five different scales into a single dimension lowers reliability. But when the unidimensional model has a better fit why should it have lower reliability with 25 items than subscales which have only five items?
Isn’t this strange?

Georg II

6

Questions and Answers / Change in item parameters across unidimensional and multidimensioanl models

« on: November 26, 2013, 03:05:07 PM »

I have analysed the same test once with a unidimensional model and once with a multidimensional model using ConQuest. In the two dimensional model the items are assigned to two dimensions. The two-dimensional model fits significantly better. However, item difficulty parameters are very different in the two models. What does this mean?
I remember I read somewhere that when item parameters across the two models are very different, it means that the better fitting model has done a better job of accounting for the data and was necessary for modeling the data. Is that right? I can’t locate the reference now. Would be thankful if you directed me to the appropriate source.

Regards
Georg II

7

Questions and Answers / Interpreting MNSQ and T fit indices

« on: August 19, 2013, 12:20:38 PM »

Dear colleagues,
How should weighted and unweighted MNSQ and T fit indices be interpreted in ConQuest?
Are the conventional .70-1.30 for MNSQ and +-2 for T applicable?
How should the confidence intervals (CI) be used? Do they help in deciding on the fit of individual items or just help have a feel of the accuracy of the MNSQ indices?

Georg
Cheers

8

Questions and Answers / Common scale in multidimensional analyses?

« on: August 19, 2013, 12:18:24 PM »

Dear colleagues,
Are person and item parameters in a multidimensional analysis in ConQuest on a common scale?
If the mean of persons on dimension 1 is .50 and on dimension 2 is .90 can we conclude that dimension 1 is harder or persons are more proficient on dimension 2?

Cheers
Georg

9

Questions and Answers / Step calibrations on the map

« on: October 26, 2012, 07:19:44 AM »

Dear all,
In a unidimensional analysis of a Likert scale with both rating scale and partial credit model, ConQuest does not provide the step calibrations on the Wright map. I get only the estimates of the items and persons.
The title of the map is " Terms in the model (Excl step terms)". Do I need a certain command to get the step calibrations on the map too?

Regards
Georg II

10

Questions and Answers / EAP reliability

« on: October 25, 2012, 08:21:27 AM »

Hallo Ray,
Can you please explain EAP reliability?
How is it computed? Can you please explain its relation with alpha and its features.
Please provide a source so that I can read up on it.

Regards
Georg II

11

Questions and Answers / Re: EAP file

« on: August 15, 2012, 06:30:24 PM »

I found this on WINSTEPS Forum.

http://www.winsteps.com/cgi-local/forum/Blah.pl?b-cc/m-1336796139/

12

Questions and Answers / Within-item multidimensional models

« on: July 26, 2012, 12:25:20 PM »

Dear Ray,

In within-item multidimensional models if we make an item load on say, five or more dimensions, aren’t we running any risks?

What consequences does it have if we make items load on 6-7 dimensions (in terms of convergence, computation, sample size requirements, fit, precision of estimates, etc.)?
I just feel that there must be some limitations from a practical point of view (if not theoretically).
Can you please comment?

Thanks
Georg II

13

Questions and Answers / EAP file

« on: July 24, 2012, 10:08:11 AM »

Hi Ray,
The EAP estimates file contains three columns for each dimension.
Can you please expalin what each colum refers to?
Under what conditions do we prefer to use EAP ability estimates instead of MLE or WLE?

Thanks

14

Questions and Answers / EAP's and PV's

« on: July 23, 2012, 12:13:53 PM »

Hi,
1. How are EAP ability estimates different from MLE and WLE?
2. When do we used EAP estimates?
3. How are PV's different from WLE, MLE, and EAP?
4. When do we used PV's?

Thanks
Georh II

15

Questions and Answers / When constarin correlations to zero?

« on: July 01, 2012, 07:20:08 AM »

Constraining correlations to zero changes the difficulty and ability parameter estimates slightly and the deviance substantially. When dimensions are free to correlate fit is better (deviance is smaller) compared to when correlations are set to zero.

When and under what conditions should we constrain correlations to zero?

Thanks