Field-normalized citation impact indicators and the choice of an appropriate counting method

TL;DR

This paper analyzes how different counting methods affect field-normalized citation impact indicators, concluding that fractional counting is necessary for proper normalization, especially in country and organization-level studies.

Contribution

It demonstrates through theoretical and empirical analysis that fractional counting is essential for accurate field normalization in bibliometric evaluations.

Findings

Full counting does not yield properly field-normalized results.

Fractional counting provides accurate field-normalized impact indicators.

Author-level and address-level fractional counting are recommended.

Abstract

Bibliometric studies often rely on field-normalized citation impact indicators in order to make comparisons between scientific fields. We discuss the connection between field normalization and the choice of a counting method for handling publications with multiple co-authors. Our focus is on the choice between full counting and fractional counting. Based on an extensive theoretical and empirical analysis, we argue that properly field-normalized results cannot be obtained when full counting is used. Fractional counting does provide results that are properly field normalized. We therefore recommend the use of fractional counting in bibliometric studies that require field normalization, especially in studies at the level of countries and research organizations. We also compare different variants of fractional counting. In general, it seems best to use either the author-level or the address-level variant of fractional counting.