Specified Formula Options
The formula gives considerable flexibility in the type of plot specification. A conditioning expression (on the right side of a | operator) always implies that different panels are used for each group. If the formula is one-sided, histograms of the variable on the right hand side of the formula, before a | operator, are displayed. If it is two-sided and both its left and right hand side variables are numeric, scatter plots are displayed. Finally, if it is two-sided and its left had side variable is a factor, box-plots of the right hand side variable by the levels of the left hand side variable are displayed.
Plot Formula Enter a formula. This can be one- or two-sided producing different plots in each case. See help file for the function plot.lme for more details.