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Mplus Discussion > Multilevel Data/Complex Sample >
 Andrew Li posted on Sunday, January 20, 2019 - 7:35 pm

I have sort of a silly question. I am looking at the interaction between two L1 variables (X and Y). The slope is fixed. I want to see whether this relationship is moderated by M, which is a L2 variable. All of these variables are continuous variables. Is this the right syntax?

usevariables = a1 x y m;
cluster = a1;
within = x;
between = m;
center x (groupmean);
analysis: type = twolevel random;
sa| y on x;
y on m;
sa on m;
output: tech1 tech3;
 Bengt O. Muthen posted on Monday, January 21, 2019 - 12:53 pm
This syntax is correct. But I would not describe it the way you do. The slope is not fixed and there isn't an interaction between two L1 variables X and Y. Instead, you have an interaction between the L1 variable X and the L2 variable M in their influence on Y.
 Andrew Li posted on Monday, January 21, 2019 - 1:14 pm
Thank you Dr. Muthen. Just to make sure, the equation I am testing is the one that has all the components for an intercept-and-slopes-as-outcomes model except for u1jX (the interaction between X and the residual for the random slope on L2).
 Bengt O. Muthen posted on Monday, January 21, 2019 - 3:35 pm
Ok, then you have

sa on m;

with zero residual variance for sa. So you can add


So that slope is not fixed, nor random - I think it is sometimes called "varying". It is varying only as a function of m.
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