  In the case of the scientometric evaluation of multi- or interdisciplinary
units one risks to compare apples with oranges: each paper has to assessed in
comparison to an appropriate reference set. We suggest that the set of citing
papers first can be considered as the relevant representation of the field of
impact. In order to normalize for differences in citation behavior among
fields, citations can be fractionally counted proportionately to the length of
the reference lists in the citing papers. This new method enables us to compare
among units with different disciplinary affiliations at the paper level and
also to assess the statistical significance of differences among sets.
Twenty-seven departments of the Tsinghua University in Beijing are thus
compared. Among them, the Department of Chinese Language and Linguistics is
upgraded from the 19th to the second position in the ranking. The overall
impact of 19 of the 27 departments is not significantly different at the 5%
level when thus normalized for different citation potentials.
