Dale J. Cohen and Jon Cohen.
The Sectioned Density Plot.
In The American Statistician, vol. 60, no. 2, pp. 167--174, 2006.

Bibtex:

@Article{        cohen:2006:TSDP,
  author = 	 "Dale J. Cohen and Jon Cohen",
  title = 	 "The Sectioned Density Plot",
  journal = 	 "The American Statistician",
  year = 	 "2006",
  volume = 	 "60",
  number = 	 "2",
  pages = 	 "167--174",
  month = 	 "May",
}