 Exponential decay growth model with E...    Message/Author  Chris Stride posted on Wednesday, June 08, 2016 - 12:18 pm
Trying to fit exponential decay growth model with estimator = bayes, can't get around this problem:

*** ERROR
For analysis with ESTIMATOR=BAYES, NEW parameters must appear on the
left-hand side in at least one MODEL CONSTRAINT equation.
No equation found containing parameter on the left-hand side: ERATE

Is there a work-around?

MODEL:
INIT BY ANX1@1;
INIT BY ANX2-ANX5* (L12-L15);

RATE BY ANX1@0;
RATE BY ANX2-ANX5* (L22-L25);

ASYMP BY ANX1@0;
ASYMP BY ANX2-ANX5* (L32-L35);

!Name means of latent vars.
[ASYMP] (AS); [INIT] (IN); [RATE@0];

MODEL CONSTRAINT:
!Create a new var equals for mean of latent rate of change.
NEW(ERATE);

L12=exp(-1*Erate); L13=exp(-2*Erate); L14=exp(-3*Erate); L15=exp(-4*Erate);

L22=(AS - IN)*1*exp(-1*Erate);
L23=(AS - IN)*2*exp(-2*Erate);
L24=(AS - IN)*3*exp(-3*Erate);
L25=(AS - IN)*4*exp(-4*Erate);

L32=1-exp(-1*Erate);
L33=1-exp(-2*Erate);
L34=1-exp(-3*Erate);
L35=1-exp(-4*Erate);  Bengt O. Muthen posted on Wednesday, June 08, 2016 - 1:00 pm
Mplus Bayes does not currently accept restrictions on parameters like here, only new, free parameters (so LHS). Don't know about a work-around except to try ML (with BS).  Chris Stride posted on Thursday, June 23, 2016 - 7:04 am
Ah... that's a shame. I'll need to stick with ML then.

The issue that I'm getting with this approach (and hence the motivation for trying Bayesian estimation) is that I keep getting a negative variance estimate for RATE (and it's not very close to zero, so no quick 'fixing to close to 0' type solution seems correct!).

I've tried fixing it to be > 0 but then I get a correlation > 1 popping up...  Bengt O. Muthen posted on Thursday, June 23, 2016 - 6:23 pm
Could you use exp(erate) instead of erate to keep it non-negative? With ML, that is.    Topics | Tree View | Search | Help/Instructions | Program Credits Administration