  Usage of field-normalized citation scores is a bibliometric standard.
Different methods for field-normalization are in use, but also the choice of
field-classification system determines the resulting field-normalized citation
scores. Using Web of Science data, we calculated field-normalized citation
scores using the same formula but different field-classification systems to
answer the question if the resulting scores are different or similar. Six
field-classification systems were used: three based on citation relations, one
on semantic similarity scores (i.e., a topical relatedness measure), one on
journal sets, and one on intellectual classifications. Systems based on journal
sets and intellectual classifications agree on at least the moderate level. Two
out of the three sets based on citation relations also agree on at least the
moderate level. Larger differences were observed for the third data set based
on citation relations and semantic similarity scores. The main policy
implication is that normalized citation impact scores or rankings based on them
should not be compared without deeper knowledge of the classification systems
that were used to derive these values or rankings.
