A primary packaging and publication module within DDI containing a Group of StudyUnits. The Group structure allows metadata regarding multiple study units to be published as a structured entity. Studies may be grouped "by design" such as a repeated study with intended areas of commonality between each study, or "ad hoc" where studies are grouped for applied or administrative reasons. When grouping is done "by design", such as within a longitudinal study, common metadata such as shared methodology, common category schemes, etc. may be moved up from the individual studies into the Group and inherited by all the members of the group. Inherited metadata may be over-ridden at the lower levels. Inheritance may be turned "off" for groups of study units done on an ad-hoc basis, such as a set of studies used for a particular activity such as instruction. The purpose of groups is described using the attributes which summarize relationships along the dimensions of time, panel, geography, instrument and language. These attributes allow the purpose to be machine-actionable, while the group also includes an element for describing the purpose in human-readable format. As a publication package Group contains a Citation, Abstract, information on authorization, the universe of the group, series statement, quality statements, ex-post evaluation material, funding and budget, purpose, coverage, analysis units covered, kind of data, other materials, a list of required resource packages and embargo information. It then allows all maintainable structures within the StudyUnit to be expressed at the Group level along with individual StudyUnits. StudyUnits may also be grouped into SubGroups allowing for infinite nesting of StudyUnits.