Fig. 6

Scatter plot of simulated data points with different spline fits from packages gam, mgcv and gamlss. Upper left: Data were fitted with library gam that calls B-spline and natural spline functions from splines package. A B-spline with 3 degrees of freedom is the default bs value. Natural splines were used also with three degrees of freedom. The two basis are different, especially in the tails of the x distribution. It is apparent that more flexibility is needed to approach the true curve, given by the dashed line. Upper right: Data fitted with library gam, with added flexibility. Both B-splines and natural splines were defined with four interior knots, resulting in a B-spline with 7 degrees of freedom and a less flexible natural spline with 5 degrees of freedom. Lower left: Comparison of data fitting at default values using function s, in packages mgcv, gam and gamlss. The thin plate regression splines are more flexible than the cubic smoothing spline used by gam and gamlss. Lower right: Comparison of data fitting at default values using P-splines. The differences are rather small and can be attributed to the different way that two packages optimize the penalty weight. Created with Code #6