Previously, I’ve written about when to choose nonlinear regression and how to model curvature with both linear and nonlinear regression. Since then, I’ve received several comments expressing confusion about what differentiates nonlinear equations from linear equations. This confusion is understandable because both types can model curves.

So, if it’s not the ability to model a curve, what *is*
the difference between a linear and nonlinear regression
equation?

## Linear Regression Equations

Linear regression requires a linear model. No surprise, right? But what does that really mean?

A model is linear...