  Ageing of publications, percentage of self-citations, and impact vary from
journal to journal within fields of science. The assumption that citation and
publication practices are homogenous within specialties and fields of science
is invalid. Furthermore, the delineation of fields and among specialties is
fuzzy. Institutional units of analysis and persons may move between fields or
span different specialties. The match between the citation index and
institutional profiles varies among institutional units and nations. The
respective matches may heavily affect the representation of the units. Non-ISI
journals are increasingly cornered into "transdisciplinary" Mode-2 functions
with the exception of specialist journals publishing in languages other than
English. An "externally cited impact factor" can be calculated for these
journals. The citation impact of non-ISI journals will be demonstrated using
Science and Public Policy as the example.
