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| Longitudinal Multi-Level Mediation |
 
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Hi,
I am trying to test a mediation hypotheses in data from a randomized clinical trial with two intervention groups. Both the outcome (y) and the proposed mediator (m) were measured four times, therefore I am using a multilevel approach. I tried to transfer example F (http://www.statmodel.com/download/Preacher.pdf) onto this longitudinal setting. I conceptualized the Cross-Level-Interaction of the treatment variable ("cond", 0/1) and time in regard of the mediator as the "a" path in my mediation model. As the "b" path I conceptualized the mean of the random slope of y on m. However, this produces an error. Where is the error in my concept (or syntax)?
This is my input:
WITHIN = time;
BETWEEN = cond;
CLUSTER = id;
STRATIFICATION = Center;
ANALYSIS: TYPE = COMPLEX TWOLEVEL RANDOM;
ALGORITHM=INTEGRATION;
INTEGRATION = MONTECARLO;
MODEL: %WITHIN%
m y;
sy|y on time;
sm|m on time;
sb|y on m;
%BETWEEN%
m y;
sm on cond(a);
sy on cond(c);
sb WITH cond m y;
[sb](b);
MODEL CONSTRAINT:
NEW(ind);
ind=a*b;
OUTPUT: TECH1 TECH8 CINTERVAL;
The error:
THE MODEL ESTIMATION DID NOT TERMINATE NORMALLY DUE TO A NON-ZERO
DERIVATIVE OF THE OBSERVED-DATA LOGLIKELIHOOD. |
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I think that on Between you also need the main effects of cond:
y on cond;
m on cond;
The time variable is probably best viewed as a moderator, so moderator formulas are relevant.
If you get non-convergence, send your output to Support along with your license number. |
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