Sub-field normalization in the multiplicative case: High- and low-impact citation indicators

Abstract

CEPR Project SCIFI-GLOW*Corresponding author. Email: jrc@eco.uc3m.esThis article uses high- and low-impact citation indicators for the evaluation of the citation per-formance of research units at different aggregate levels using a dataset of about 3.6 millionarticles published in 1998–2002 in the natural and the social sciences with a 5-year citationwindow. The difficulty is that a large proportion of individual articles are assigned to multiplesubfields. To control for wide differences in citation practices at the subfield level, we apply anovel normalization procedure in the multiplicative approach in which each paper is whollycounted as many times as necessary in the several categories to which it is assigned at eachaggregation level. The methodology is applied to a partition of the world into three geographicalareas: the USA, the European Union (EU), and the Rest of the World. The main findings are thefollowing two. (1) Although normalization does not systematically bias the results against anyarea, it reduces the US/EU high-impact gap in the all-sciences case by a non-negligible 14.4%.(2) The dominance of the USA over the EU in the basic and applied research published in theperiodical literature is almost universal at all aggregation levels. From the high-impact perspective,for example, the USA is ahead of the EU in 77 out of 80 disciplines, and all of 20 fields. For allsciences as a whole, the US high-impact indicator is 61% greater than that of the EU.Keywords: citation analysis; high- and low-impact indicators; subfield normalization; multiplica-tive approach; US/EU scientific gap.