The GAM Procedure

Overview: GAM Procedure

The GAM procedure fits generalized additive models as defined by Hastie and Tibshirani (1990). This procedure provides powerful tools for nonparametric regression and smoothing.

Nonparametric regression relaxes the usual assumption of linearity and enables you to uncover relationships between the independent variables and the dependent variable that might otherwise be missed. SAS provides many procedures for nonparametric regression, such as the LOESS procedure for local regression and the TPSPLINE procedure for thin-plate smoothing splines. The generalized additive models fit by the GAM procedure combine the following:

an additivity assumption (Stone, 1985) that enables relatively many nonparametric relationships to be explored simultaneously
the distributional flexibility of generalized linear models (Nelder and Wedderburn, 1972)

Thus, you can use the GAM procedure when you have multiple independent variables whose effect you want to model nonparametrically, or when the dependent variable is not normally distributed. See the section Nonparametric Regression for more details on the form of generalized additive models.

The GAM procedure does the following:

provides nonparametric estimates for additive models
supports the use of multidimensional data
supports multiple SCORE statements
fits both generalized semiparametric additive models and generalized additive models
enables you to choose a particular model by specifying the model degrees of freedom or smoothing parameter
produces graphs with ODS Graphics