Cross-cultural studies is the third form of cross-cultural comparisons. The first is comparison of case studies, the second is controlled comparison among variants of a common derivation, and the third is comparison within a sample of cases. Unlike comparative studies, which examines similar characteristics of a few societies, cross-cultural studies uses a sufficiently large sample so that statistical analysis can be made to show relationships or lack of relationships between the traits in question. These studies are surveys of ethnographic data.