Scatter Plots - R Graphics - page 120

Figure 5-21. Left: LOESS fit lines for each group; right: extrapolated linear fit lines

Notice that the blue line, for males, doesn't run all the way to the right side of the graph. There
are two reasons for this. The first is that, by default, stat_smooth() limits the prediction to
within the range of the predictor data (on the x-axis). The second is that even if it extrapolates,
the loess() function only offers prediction within the xrange of the data.
If you want the lines to extrapolate from the data, as shown in the right-hand image of
Figure 5-21 , you must use a model method that allows extrapolation, like lm() , and pass
stat_smooth() the option fullrange=TRUE :

sps + geom_smooth(method = lm, se = FALSE FALSE , fullrange = TRUE TRUE )

In this example with the heightweight data set, the default settings for stat_smooth() (with
LOESS and no extrapolation) make more sense than the extrapolated linear predictions, because
we don't grow linearly and we don't grow forever.

Adding Fitted Lines from an Existing Model

Problem
You have already created a fitted regression model object for a data set, and you want to plot the
lines for that model.