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Additive model

Statistical regression model

In statistics, an additive model (AM) is a nonparametric regression method. It was suggested by Jerome H. Friedman and Werner Stuetzle (1981) and is an essential part of the ACE algorithm. The AM uses a one-dimensional smoother to build a restricted class of nonparametric regression models. Because of this, it is less affected by the curse of dimensionality than a p-dimensional smoother. Furthermore, the AM is more flexible than a standard linear model, while being more interpretable than a general regression surface at the cost of approximation errors. Problems with AM, like many other machine-learning methods, include model selection, overfitting, and multicollinearity.

01Description

Given a data set \{y_{i},\,x_{i1},\ldots ,x_{ip}\}_{i=1}^{n} of n statistical units, where \{x_{i1},\ldots ,x_{ip}\}_{i=1}^{n} represent predictors and y_{i} is the outcome, the additive model takes the form

\mathrm {E} [y_{i}|x_{i1},\ldots ,x_{ip}]=\beta _{0}+\sum _{j=1}^{p}f_{j}(x_{ij})

or

Y=\beta _{0}+\sum _{j=1}^{p}f_{j}(X_{j})+\varepsilon

Where \mathrm {E} [\epsilon ]=0, \mathrm {Var} (\epsilon )=\sigma ^{2} and \mathrm {E} [f_{j}(X_{j})]=0. The functions f_{j}(x_{ij}) are unknown smooth functions fit from the data. Fitting the AM (i.e. the functions f_{j}(x_{ij})) can be done using the backfitting algorithm proposed by Andreas Buja, Trevor Hastie and Robert Tibshirani (1989).

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