
Message/Author 

Anne Chan posted on Wednesday, December 29, 2010  2:47 pm



Hello! I run a LPA on three variables. Comparing 1 to 3 classes solution, the 3 classes solution is the best and it works perfectly fine. However, when I go for the 4 classes solution. There is a error message: "THE STANDARD ERRORS OF THE MODEL PARAMETER ESTIMATES MAY NOT BE TRUSTWORTHY FOR SOME PARAMETERS DUE TO A NONPOSITIVE DEFINITE FIRSTORDER DERIVATIVE PRODUCT MATRIX. THIS MAY BE DUE TO THE STARTING VALUES BUT MAY ALSO BE AN INDICATION OF MODEL NONIDENTIFICATION. THE CONDITION NUMBER IS 0.514D18. PROBLEM INVOLVING PARAMETER 11. From the output file, I see that 1 group only have 1 case in it. May I ask what does this means? Is that the 4 classes solution does not fit the data? Can I still continue my project with the 3class solution in this case? Thanks! 


If your 4class solution has its best loglikelihood value replicated several times so you believe you have reached the best maximum, then this 4class solution is not useful and you should proceed with 3 classes. A 4class solution like that can happen for instance if you let the variances differ across classes, but also in other cases. The one person is like an outlier. 

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