Moderated mediation in MLM PreviousNext
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 Amy Christie posted on Wednesday, April 29, 2009 - 4:50 pm
We would like to test a moderated mediation model. We have a level 1 X variable, and level 1 mediator (M), and a level 1 Y variable. Our moderator is a level 2 variable. I am aware of the following method to test the 1-1-1 indirect effects with level 2 moderators:

Bauer, D. J., Preacher, K. J., & Gil, K. M. (2006). Conceptualizing and testing random indirect effects and moderated mediation in multilevel models: New procedures and recommendations. Psychological Methods, 11, 142-163.

However, we were wondering if it is a straightforward extension to also include a test of the 2-1-1 indirect effect? We want to now whether our level 2 variable also influences Y through M(under certain conditions of X).

Is it possible to test this model with Mplus, and how?

Thank you; we appreciate your help.
 Kristopher J. Preacher posted on Thursday, April 30, 2009 - 2:01 pm
This is for a 2-1-1 model in which the 'b' path of the mediation model is random, and moderated by a Level-2 variable W. I tried it out on real data and it seems to work:

TITLE: 2-1-1 moderated mediation model
DATA: FILE IS bpg_example_data_modmed.dat;
VARIABLE: NAMES ARE id x m y xm mm ym w;
USEVARIABLES ARE id m y xm w;
CLUSTER IS id;
BETWEEN ARE xm w;
ANALYSIS: TYPE = TWOLEVEL RANDOM;
MODEL:

!2-1-1 moderated mediation with random b slope
!in which b is moderated by W.
%WITHIN%
m y;
sb | y ON m;
%BETWEEN%
xm m y sb w;
[sb](b1);
sb WITH xm m y;
w WITH xm m;
m ON xm(a);
y ON m(b1);
y ON xm w;
sb ON w(b3);
MODEL CONSTRAINT:
NEW(ind1 ind2 ind3);
ind1=a*(b1+b3*.1); ! indirect effect conditional on W = .1
ind2=a*(b1+b3*.5); ! indirect effect conditional on W = .5
ind3=a*(b1+b3*.9); ! indirect effect conditional on W = .9
OUTPUT: CINTERVAL;

Additional Mplus code for similar models, including the 1-1-1 model from Bauer et al. (2006) can be found here:

http://www.people.ku.edu/~preacher/syntax_appendix_042509.pdf
 Amy Christie posted on Friday, May 01, 2009 - 2:08 pm
Thank you - this is very helpful (as is the link).
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