In some applications it is cost efficient to sample data in two or more stages. In the first stage a simple random sample is drawn and then stratified according to some easily measured attribute. In ...

Mary Hall is a editor for Investopedia's Advisor Insights, in addition to being the editor of several books and doctoral papers. Mary received her bachelor's in English from Kent State University with ...

Greg DePersio has 13+ years of professional experience in sales and SEO and 3+ years as a writer and editor. Robert Kelly is managing director of XTS Energy LLC, and has more than three decades of ...