The group of persons or other elements that are the object of research and to which any analytic results refer. Age, nationality, and residence commonly help to delineate a given universe, but any of a number of factors may be involved, such as sex, race, income, veteran status, criminal convictions, etc. The universe may consist of elements other than persons, such as housing units, court cases, deaths, countries, etc. In general, it should be possible to tell from the description of the universe whether a given individual or element (hypothetical or real) is a member of the population under study. If all the variables/nCubes described in the data documentation relate to the same population, e.g., the same set of survey respondents, this element would be unnecessary at data description level. In this case, universe can be fully described at the study level. For forward-compatibility, DDI Lifecycle XHTML tags may be used in this element. This element may be repeated only to support multiple language expressions of the content. To specify the use of a Controlled Vocabulary or standard concept use the internal element "concept". If multiple concepts are needed the parent element should be replicated. Internal text related to each concept should be allocated to accompany the relevant concept.