I have a question in relation to testlets. I wish to do EFA and CFA on some data where several of the variables are testlets (common stem and between 3 and 7 parts related to the stem). I have been told that testlets can affect the factor analyses but that Mplus can take the potential effect of testlets into account. I would be grateful if you can tell me how to go about this or else if you could direct me to this information elsewhere in the discussion forum (if it exists. I searched and could not find it).
Seán Delaney posted on Tuesday, February 05, 2008 - 10:00 pm
I want to add one thing to my previous question about testlets and factor analysis. My data are categorical (binary). Thanks.
It sounds like you have testlets made up of sets of binary items. The choice of items is crucial in creating testlets. Mplus cannot help with that. Mplus can take measurement error into account when using testlets as factor indicators in factor analysis. You can also use the original binary items as factor indicators in Mplus.
Seán Delaney posted on Wednesday, February 06, 2008 - 3:48 pm
Thanks for this reply Linda.
Can you direct me to information on how to take measurement error into account when using testlets as factor indicators in factor analysis and when entering such data into the data file?
so the probability of getting response c in item j and from person i depends on some appropriate link function G, item parameters a_j and b_j and a person parameter theta_i and the testlet effect gamma_ik (where item j belongs to testlet k).
So it looks like a bi-factor model, also called a general-factor, specific-factor model. The Mplus course Topic 1 gives the input for that with continuous items, but it is the same idea for categorical items. Except, your model imposes equality of the slope for the general factor (theta) and the specific factor (gamma).
Jing Davis posted on Wednesday, August 29, 2018 - 9:39 am
Dear Dr. Muthen,
I was running an analysis, which has two testlets in the data. The structure I set up is: MODEL: T1 BY V4 V5 V6 V7 V8 V18; T2 BY V13 V14 V15 V16 V17 V19; G BY V1-V22; G WITH T1@0T2@0; T1 WITH T2@0;
My question is: As for a testlet model, whether I should put T1 T2 as factor indicators in the Command line, such as: G BY T1 T2 V1-V22.
Ryan Veal posted on Wednesday, January 16, 2019 - 6:06 pm
Hi Prof. Muthen,
I'm trying to work out the syntax for a CFA model using testlets and latent variables, and the above discussion thread doesn't answer my question.
I can't quite work out how to include testlets as factor indicators in a factor analysis model. For the model in question, each testlet would load on the latent factor, as would another separate item. I have provided the below syntax as a guide for the model i am referring to:
MODEL: F1 BY ITEM1 (TESTLET BY ITEM2 AND ITEM3); F2 BY ITEM5 (TESTLET BY ITEM4 AND ITEM6); F3 BY ITEM9 (TESTLET BY ITEM7 AND ITEM10); G BY F1 F2 F3;
I have tried to create separet indicators using the testlets as indicators without success. Are you able to provide a brief answer?
I assume the testlets are sums of items. If so, you can create them in Define. And then you simply refer to these new variables on the Usevariable list and in your BY statements (together with other items loading on the factor). I am not sure if that is what you are asking, however.