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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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