The notion of mixed membership arises naturally in the context of multivariate data analysis when attributes collected on individuals or objects originate from a mixture of different categories or components. Consider, for example, an individual with both European and Asian ancestry whose mixed origins correspond to a statement of mixed membership: “1/4 European and 3/4 Asian ancestry.” This description is conceptually very different from a probability statement of “25% chance of being European and 75% chance of being Asian”.