ABSTRACT
Grouped data arise in almost all areas of statistical application. Sometimes the grouping structure is simple, where each case belongs to a single group and there is only one grouping factor. More complex datasets have a hierarchical or nested structure or include longitudinal or spatial elements. Sometimes the grouping arises because the same individual is measured repeatedly or sometimes each individual is measured once only but these individuals have some form of group structure. We defer examination of the repeated measurement of individuals to the next chapter, although the statistical methodology used is the same.
