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Prof. Muthen, I have the following model to estimate Y2, Y3, Y4 = g(eta1) (g is a vector function) eta1 = h(X2) Y1 = f(X1, eta1) Where eta1 is a continuous latent variable and Y2, Y3, Y4 are ordinal indicators capturing eta1. Y1 is BINARY and the variable of primary interest. X’s are exogenous variables. We have sample selection issue. I was wondering whether it would be OK to use IMR (inverse mills ratio) as one of the explanatory variable in Y1 equation and then use WLSMV. I am calculating IMR from the selection model; Z = z(X4) Could you kindly suggest me some related references? Thanking you. 


This sounds like a reasonable approach. You may want to model the heteroscedasticity of your y1 residuals. 


Thank you Madam. Checking heteroscedasticity in equation Y1 is in fact a good idea. Could you kindly suggest me an example to handle heteroscedasticity using MPlus. Regards 


I can think of 2 approaches that could be useful. One draws on UG ex3.9. The other draws on UG ex5.3 with CONSTRAINT = x, where the heteroscedasticity is a function of the covariate x. But you would have to explore. 


Dear Prof. Muthen, I have a simple question. I would like to select only some groups of the sample from the main dataset and save it for another analysis. Please could you advise what command that I can use. Thanks. 


You can select observations using the USEOBSERVATIONS option of the VARIABLE command. If you want to save that data set, use the FILE option of the SAVEDATA command. 


Dear Linda, Thanks for the advise. I had tried this but the saved file contained no data. Please suggest. Here is the command. DATA: File is C:\mplus\batch1.dat Variable: names are ...(I have all the variables in the dataset written here including w1 which is used in useobservation command)...; Useobservation = w1 EQ 1; Savedata: File is C:\mplus\w1; I got the file out of the run but there is no data in the file. It is supposed to be about 600 observations here. Thanks. 


Please send the relevant files and your license number to support@statmodel.com. 


I am interested in using the NOBSERVATIONS option to select a subset (N) of a simulated dataset. The manual indicates that the first N cases in the dataset would be selected. Is it possible to select a random sample of cases using the NOBSERVATIONS option? If all else fails I can create randomized groups the dataset and use the USEOBSERVATIONS option, but this does not seem any more appealing (to me) than just using the first N cases (in this case). Thank you for any clarification/assistance. 


Mplus does not have an option for random sampling from a data set. You would need to do that outside of Mplus. 


Thank you for your quick response. 

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