## Regression methods available in CanoDraw

When you want to summarize relations between variables by a regression model, you can fit the model with either one predictor (in this case the model is represented by the fitted line or curve) or with two predictors (the fitted model is then represented by a contour plot). CanoDraw allows you to fit following types of regression models:
• Generalized linear models (GLM) - this is now a widely used family of models, providing support for linear models where the response variables represent counts, relative frequencies, probabilities, or physical measurements like dimensions or weight. Such variables cannot be assumed to have a constant variance - an assumption of the classical linear regression. CanoDraw supports the standard distribution families (Poisson, Binomial, Gamma, Gaussian) and supports the canonical link functions for each of them (in addition, log link function selection is available for Gamma distribution). The effects of predictor(s) can be specified as purely linear or as a second or third degree polynomial. CanoDraw also offers a simple form of stepwise selection of model complexity, using either the classical tests based on analysis of deviance or model selection based on AIC statistics.

• Generalized additive models (GAM) - generalized additive models replace the linear terms of individual predictors, as used in GLMs, with smooth terms, where only the complexity, not the exact "shape" of predictor influence is specified. CanoDraw supports cubic-spline based smooth terms and standard distribution / link function assumptions - the same as for GLMs. Stepwise selection of smooth term(s) complexity, using the AIC statistics, is also supported.

• Loess smoother - represents an universal, reliable smoothing method, based on local, weighted linear (or second-order polynomial) regression. CanoDraw makes available some enhancement known from other software (namely the S and R statistical systems) - dropping the square term and making a conditionally parametric fit.

For all the fitted regression models, CanoDraw supports creation of simple regression diagnostic diagrams - the residuals (optionally their absolute value) can be plotted either against the fitted values or against the predictors.