QUADRATIC NONLINEAR EFFECT PreviousNext
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 crystal posted on Sunday, December 07, 2014 - 12:45 pm
Hi I am trying to create a SEM model with a quadratic effect between my mediating variable and my outcome variable
(X1, X2 AND X3) all predict mediating variable and the mediating variable predicts Y1
X1------
X2----- mediating variable ------ Y1
X3-----

i want to model a quadratic relationship between mediating variable and y1. do i just add a power term of mediating variable (squared) and have it predict Y1? Also, do i need my exogenous variables predicting the squared term?
 Bengt O. Muthen posted on Tuesday, December 09, 2014 - 11:57 am
Create m2 in Define:

Define:
m2 = (m-mbar)*(m-mbar); !mbar = mean

Then use

Model:
y on m m2;
m on x1-x3;

Here, m2 will be a covariate and automatically correlated with x1-x3.

Because of the non-linearity I would ignore the chi-square testing.
 Bengt O. Muthen posted on Tuesday, December 09, 2014 - 11:59 am
Also, the indirect effect estimation is not straightforward in this case. Perhaps it could be derived from my paper on our website:

Muthén, B. (2011). Applications of causally defined direct and indirect effects in mediation analysis using SEM in Mplus.
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