  We present an empirical comparison between two normalization mechanisms for
citation-based indicators of research performance. These mechanisms aim to
normalize citation counts for the field and the year in which a publication was
published. One mechanism is applied in the current so-called crown indicator of
our institute. The other mechanism is applied in the new crown indicator that
our institute is planning to adopt. We find that at high aggregation levels,
such as at the level of large research institutions or at the level of
countries, the differences between the two mechanisms are very small. At lower
aggregation levels, such as at the level of research groups or at the level of
journals, the differences between the two mechanisms are somewhat larger. We
pay special attention to the way in which recent publications are handled.
These publications typically have very low citation counts and should therefore
be handled with special care.
