I'm trying to draw violin plots and wondering if there is an accepted best practice for scaling them across groups. Here are three options I've tried using the R mtcars
data set (Motor Trend Cars from 1973, found here).
Equal Widths
Seems to be what the original paper* does and what R vioplot
does (example). Good for comparing shape.
Equal Areas
Feels right since each plot is a probability plot, and so the area of each should equal 1.0 in some coordinate space. Good for comparing density within each group, but seems more appropriate if the plots are overlaid.
Weighted Areas
Like equal area, but weighted by number of observations. 6-cyl gets relatively thinner since there are fewer of those cars. Good for comparing density across groups.
*Violin Plots: A Box Plot-Density Trace Synergis (DOI: 10.2307/2685478)