Pareto Chart is a bar graph used to arrange information in such a way that priorities for process improvement can be established.
Purposes:
* To display the relative importance of data.
* To direct efforts to the biggest improvement opportunity by highlighting the vital few in contrast to the useful many.
More reading:
http://www.kfmaas.de/q_pareto.html
http://www.dartmouth.edu/~ogehome/CQI/Pareto.html