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Mplus Discussion > Structural Equation Modeling >
 Stefanie Hinkle posted on Tuesday, August 16, 2011 - 2:40 pm
Hi. I running a path model to examine the relationship between x and y while including covariates and mediators. I would like to account for a non-linear relationship between x and y, as indicated when I examine the relationship using ordinary regression. Do you have any recommendations on how to best account for a non-linear relationship? I have tried to include X^2 in the model, having it modeled just as X is and allowing the two to covary. However the model is non-positive definite when I do this.

I have also considered including an additional term for piecewise regression. Would it follow the normal X term and do they covary?

Any advice that you could provide would be very helpful!

Thanks so much!
 Bengt O. Muthen posted on Wednesday, August 17, 2011 - 11:32 am
Instead of X and X^2 try using Z and Z2,

Z = X-X_bar
Z2 = Z*Z

where X_bar is the sample mean of X. If that gives an error, send to support.
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