A second vector of summary statistics (also from Describe)
labels
name the pair
pos
Labels are located where with respect to the mean?
arrow.len
Arrow length
...
Other parameters for plot
Details
For an example of two way error bars describing the effects of mood manipulations upon positive and negative affect, see http://personality-project.org/revelle/publications/happy-sad-appendix/FIG.A-6.pdf)