Non-linear Models

In linear regression the mean surface in sample space is a plane; in non-linear regression it may be an arbitrary curved surface but in all other respects the models are same. Fortunately in practice the mean surface in most non-linear regression models will be approximately planar in the region of highest likelihood, allowing some good approximations based on linear regression techniques to be used, but non-linear regression models can still present tricky computational and inferential problems.