curvilinear relationship

Regression Models:How do you know you need a polynomial?

April 3rd, 2009 by

A polynomial term–a quadratic (squared) or cubic (cubed) term turns a linear regression model into a curve.  But because it is X that is squared or cubed, not the Beta coefficient, it still qualifies as a linear model.  This makes it a nice, straightforward way to model curves without having to model complicated non-linear models.

But how do you know if you need one–when a linear model isn’t the best model? (more…)