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A negative variance/residual variance... |
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Ping Li posted on Wednesday, December 26, 2012 - 4:02 pm
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Hi Linda, I run a second-order lgc with two time points. My model is below: MODEL: LN1 BY LN11* LN12 LN13 ; VT1 BY VT11* VT12 VT13 ; LN1@1 VT1@1; f1 BY LN1@1 VT1 (1); f1@1; LN2 BY LN21* LN22 LN23 ; VT2 BY VT21* VT22 VT23 ; LN2@1 VT2@1; f2 BY LN2@1 VT2 (1); f2@1; [LN11 LN21] (2); [ VT11 VT21] (3); [LN12 LN22] (4); [VT12 VT22] (5); [LN13 LN23](6); [VT13 VT23] (7); [LN1 LN2](8); [VT1 VT2](9) i s |f1@0 f2@1; Then I got an warning: WARNING: THE LATENT VARIABLE COVARIANCE MATRIX (PSI) IS NOT POSITIVE DEFINITE. THIS COULD INDICATE A NEGATIVE VARIANCE/RESIDUAL VARIANCE FOR A LATENT VARIABLE, CHECK THE TECH4 OUTPUT FOR MORE INFORMATION. PROBLEM INVOLVING VARIABLE I. Is it okay with negative variance? Thanks very much! Ping |
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No, a negative variance means the model is not admissible. If it is very small and not significant, you can fix it at zero. A linear model cannot be identified for only two time points. You need at least three. |
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Ping Li posted on Thursday, December 27, 2012 - 12:13 pm
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Thanks very much, Linda! Happy Holiday! |
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