Hello, I have got a problem and wondering if someone can help me please. I am trying Proc Mixed with the random intercept: and getting a problem. I have done multiple imputation (so, there are 10, for example _imputation_ = 1 ...._imputation_ = 10). The proc mixed is as follows (variable names are just for example): proc sort data = reg_fin_1 ; by _imputation_ ID ; run; proc mixed data = reg_fin_1 noitprint PLOTS(MAXPOINTS= 20000000000) ; class ID ; by _imputation_ ; model Y = x1 x2 x3 /solution ddfm = bw residual ; random intercept / subject = NEW_PIN type = un ; ods output solutionF=mxparms3 ; run; The problem is that I get the following message: Estimated G matrix is not positive definite. The above message was for the following BY group: _imputation_=1 Estimated G matrix is not positive definite. The above message was for the following BY group: _imputation_=2 ...... ....... However, I don't get this notice when I run proc mixed with the complete cases: I mean, excluded the missing values, hence no imputation, and unlike the multiple imputation I have one dataset. Thanks to all. Rahid
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