  The journal impact factor is not comparable among fields of science and
social science because of systematic differences in publication and citation
behaviour across disciplines. In this work, a source normalization of the
journal impact factor is proposed. We use the aggregate impact factor of the
citing journals as a measure of the citation potential in the journal topic,
and we employ this citation potential in the normalization of the journal
impact factor to make it comparable between scientific fields. An empirical
application comparing some impact indicators with our topic normalized impact
factor in a set of 224 journals from four different fields shows that our
normalization, using the citation potential in the journal topic, reduces the
between-group variance with respect to the within-group variance in a higher
proportion than the rest of indicators analysed. The effect of journal
self-citations over the normalization process is also studied.
