For academic libraries, peer groups are formed according to the type of library.

Libraries in universities of applied sciences differ from university libraries in terms of resources and tasks profile. They form the first category.

The second category comprises the so-called "one-layered" university libraries. They consist of a central library with branches that form one organizational unit. Statistical data is gathered for the system as a whole.

The third category comprises the so-called "two-layered" university libraries. They consist of a central library (sometimes with branches) and additionally of independent libraries in institutes or faculties. Statistical data is gathered only for the central library. A clear distinction between the two is not always possible.