The questions of output in mixture m... PreviousNext
Mplus Discussion > Latent Variable Mixture Modeling >
Message/Author
 Ali posted on Tuesday, February 18, 2014 - 3:20 am
Hello
I am using Mixture IRT model to fit 1 calss, 2 class, and 3 class with 20 data set.
In 2 class, there is no any problem to fit, also, THE BEST LOGLIKELIHOOD VALUE HAS BEEN REPLICATED. But , in 3 class , sometimes it showed THE BEST LOGLIKELIHOOD VALUE HAS BEEN REPLICATED , but meanwhile shows :THE STANDARD ERRORS OF THE MODEL PARAMETER ESTIMATES MAY NOT BE TRUSTWORTHY FOR SOME PARAMETERS DUE TO A NON-POSITIVE DEFINITE FIRST-ORDER DERIVATIVE PRODUCT MATRIX.; and :ONE OR MORE PARAMETERS WERE FIXED TO AVOID SINGULARITY OF THE INFORMATION MATRIX.;
Are results trustful such item parameters and the values of BIC? Or does it mean that model can・t fit the data?
In addition, sometimes the results of 3 classes showed :THE BEST LOGLIKELIHOOD VALUE WAS NOT REPLICATED. : and I increased the starting value = 100 20 to 1000 200 , but it still showed that :THE BEST LOGLIKELIHOOD VALUE WAS NOT REPLICATED. : Does that mean the model can・t fit the data too? Or should I increase starting values more?
 Linda K. Muthen posted on Tuesday, February 18, 2014 - 12:15 pm
The best loglikelihood must be replicated. Even when it is replicated, there can be other problems. I would need to see the output with the error message and your license number at support@statmodel.com to determine what the problem is.
 Ali posted on Monday, February 24, 2014 - 1:45 pm
Thanks!
Can I obtain the estimate of individual ability while I am using mixture IRT model?
Or, I just can only get the membership and mean of group ability ?
 Bengt O. Muthen posted on Monday, February 24, 2014 - 9:23 pm
You get the individual ability estimate for each latent class and also the ability estimate mixed over classes. For a factor names F, they are called F_C and F, respectively.
 Ali posted on Monday, February 24, 2014 - 10:49 pm
So, do you mean the output which I can get the the estimated of ability for each class and the whole sample's estimated ability ?
But, could I get the estimated of ability of each person in a class?
For example, if there are 200 people in class 1 , could I also get 200 people's estimated ability in class 1?
 Bengt O. Muthen posted on Tuesday, February 25, 2014 - 5:38 pm
I am talking about each person's factor score - you get 2 versions of each person's factor score (class-specific and mixed over classes).

You get that using the Savedata command and Save - fscores.
 Ali posted on Tuesday, March 04, 2014 - 1:04 am
Thank you.
I am trying to find the fitted model in a mixture Rasch model. I fitted the data in 2 classes , 3 classes and 4 classes. BIC for 2,3,4 classes are 45190.796,45053.329 45083.17.From the BIC value, 3 classes should fit well, but the output gave me the message"ONE OR MORE PARAMETERS WERE FIXED TO AVOID SINGULARITY ...".
Should I choose the 3- classes model?
 Linda K. Muthen posted on Tuesday, March 04, 2014 - 12:00 pm
It depends which parameter was fixed and why. Please send the output and your license number to support@statmodel.com.
Back to top
Add Your Message Here
Post:
Username: Posting Information:
This is a private posting area. Only registered users and moderators may post messages here.
Password:
Options: Enable HTML code in message
Automatically activate URLs in message
Action: