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I am intersted in fitting Fox et al (2007) model of speed and accuracy. Accuracy is modeled using a 2 parameter IRT model and speed is modeled using a lognormal model. The two models are combined in a hierarchical framework. http://www.jstatsoft.org/v20/i07/paper What is the script for doing this in Mplus? Thanks! 


Here is a sample code with 3 items. variable: names=U1U3 T1T3; categorical=U1U3; usevar=U1U3 logT1logT3; define: logT1=log(T1); logT2=log(T2); logT3=log(T3); model: theta by U1U3; ! accuracy speed by logT1logT3; ! speed 

Maya Greene posted on Wednesday, March 11, 2015  3:09 pm



Hi Tihomir, thanks for your answer. I am confused about how the multilevel structure of the data (trials nested within person) would be modeled here. 


You can add multilevel model but the paper you referred to doesn't have a multilevel model. Items are nested within person. I don't see multiple trials by the same person on the same item. The hierarchical discussion in that paper seems to be regarding priors. In Mplus you can do the above model using ML, Bayes or WLSMV estimators. Take a look at Mplus user's guide examples 9.6 and 9.7 for possible multilevel modeling. 

Maya Greene posted on Thursday, March 12, 2015  6:25 pm



Thank you for the reference. I looked at the examples and I believe I'll be able to work something out with them. 

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