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| Warning Message: Non-positive definit... |
 
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| Megan McVay posted on Tuesday, March 14, 2017 - 10:11 am
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Help w/ this message
“THE STANDARD ERRORS OF THE MODEL PARAMETER ESTIMATES MAY NOT BE TRUSTWORTHY FOR SOME PARAMETERS DUE TO A NON-POSITIVE DEFINITE FIRST-ORDER DERIVATIVE PRODUCT MATRIX. THIS MAY BE DUE TO THE STARTING VALUES BUT MAY ALSO BE AN INDICATION OF MODEL NONIDENTIFICATION. THE CONDITION NUMBER IS 0.173D-18. PROBLEM INVOLVING PARAMETER 40.”
Our model:
Autoregressive mediation model to see if treatment effects are mediated by psychosoc variables. 3 mediators @t2 predicting outcomes @t3,controlling for t0.
Model:
outcomet3 on outcomet0 RamdomizationGroup mediatorAt2 mediatorBt2 mediatorCt2;
MediatorAt2 on RamdomizationGroup MediatorAt0;
MediatorBt2 on RamdomizationGroup MediatorBt0;
MediatorCt2 on RamdomizationGroup MediatorCt0;
Randomizationgroup with outcomet0 mediatorAt0 mediatorBt0 mediatorCt0;
Outcomet0 with mediatorAt0 mediatorBt0 mediatorCt0;
mediatorAt0 with mediatorBt0 mediatorCt0;
mediatorBt0 with mediatorCt0;
mediatorBt2 with mediatorCt2;
Variables are continuous except RandomizationGroup. Parameter 40 is variance of outcomet0. Model fit=good.
We noticed big variance in outcome and big correlation of outcome @t0 & t3, so we tried w/ no luck:
1 Dropping outcomet0 from model
2 Using difference score(t3-t0) as outcome
3 Log transforming outcome(error message becomes covariance of outcomet0/mediatorCt0)
4 1 mediator only |
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