Publication: Sub-field normalization in the multiplicative case : average-based citation indicators
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2012-01
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Abstract
This paper investigates the citation impact of three large geographical areas –the U.S., the
European Union (EU), and the rest of the world (RW)– at different aggregation levels. The
difficulty is that 42% of the 3.6 million articles in our Thomson Scientific dataset are assigned to
several sub-fields among a set of 219 Web of Science categories. We follow a multiplicative
approach in which every article is wholly counted as many times as it appears at each aggregation
level. We compute the crown indicator and the Mean Normalized Citation Score (MNCS) using for
the first time sub-field normalization procedures for the multiplicative case. We also compute a
third indicator that does not correct for differences in citation practices across sub-fields. It is found
that: (1) No geographical area is systematically favored (or penalized) by any of the two normalized
indicators. (2) According to the MNCS, only in six out of 80 disciplines –but in none of 20 fields– is
the EU ahead of the U.S. In contrast, the normalized U.S./EU gap is greater than 20% in 44
disciplines, 13 fields, and for all sciences as a whole. The dominance of the EU over the RW is even
greater. (3) The U.S. appears to devote relatively more –and the RW less– publication effort to subfields
with a high mean citation rate, which explains why the U.S./EU and EU/RW gaps for all
sciences as a whole increase by 4.5 and 5.6 percentage points in the un-normalized case. The results with a fractional approach are very similar indeed