The aim of this study is to analyze to which extent the Journal Impact Factor (JIF)
reflects the amount of excellent publications contained in a journal in the corresponding
subject category. We are introducing two percentile-based indicators in order to measure
the excellence contribution at journal level. Calculations of these indicators have
been carried out for twenty different Journal Citation Reports (JCR) subject categories
to investigate the correlation with Garfield's Journal Impact Factor. Differences
in the ranking according to all three indicators especially in First Quartile (Q1)
of each category are shown and discussed. We have also studied the effect of multidisciplinary
journals to the excellence contribution at category level and observed considerable
differences between the twenty considered categories under analysis. Their omission
would lead to neglect a large part of excellent publications, especially in the hard
sciences. The introduced excellence indicators are very robust considering the types
of documents considered for their calculation. The results of this study show that
the journal excellence content is not completely reflected in the JIF measure and
affects both Science and Social Science Edition categories. Therefore, the introduction
of journal excellence indicators will help to give a more complete picture of the
citation impact of a journal, because they are informing directly about the total
and normalized excellence contribution of each journal to the corresponding subject
category. They are a valuable enrichment and complement of the JIF, and more suitable
than the Journal Citation Indicator, recently added to the JCR, because they reflect
the inherent skewness of the citation distribution.
