precedes has_specified_input has_specified_output executes material processing population material sampling process population stratification prior to sampling 2 1 Orlaith Burke Alejandra Gonzalez-Beltran PRS+AGB adapted from wikipedia: http://en.wikipedia.org/wiki/Stratified_sampling polled on June 7th,2013 Philippe Rocca-Serra stratification is a planned process which executes a stratification rule using as input a population and assign it member to mutually exclusive subpopulation based on the values defined by the stratification rule stratifying population stratification rule ready for release