Measuring contextual citation impact of scientific journals

TL;DR

This paper introduces SNIP, a new indicator for journal citation impact that accounts for field-specific citation behaviors, enabling fairer cross-field comparisons of journal influence.

Contribution

It develops and validates SNIP, a normalized impact measure that adjusts for differences in citation practices across scientific fields.

Findings

SNIP varies significantly across disciplines and journal types.

SNIP enables more equitable comparison of journal impact across fields.

Empirical analysis based on Elsevier's Scopus data supports SNIP's effectiveness.

Abstract

This paper explores a new indicator of journal citation impact, denoted as source normalized impact per paper (SNIP). It measures a journal's contextual citation impact, taking into account characteristics of its properly defined subject field, especially the frequency at which authors cite other papers in their reference lists, the rapidity of maturing of citation impact, and the extent to which a database used for the assessment covers the field's literature. It further develops Eugene Garfield's notions of a field's 'citation potential' defined as the average length of references lists in a field and determining the probability of being cited, and the need in fair performance assessments to correct for differences between subject fields. A journal's subject field is defined as the set of papers citing that journal. SNIP is defined as the ratio of the journal's citation count per paper and the citation potential in its subject field. It aims to allow direct comparison of sources in different subject fields. Citation potential is shown to vary not only between journal subject categories - groupings of journals sharing a research field - or disciplines (e.g., journals in mathematics, engineering and social sciences tend to have lower values than titles in life sciences), but also between journals within the same subject category. For instance, basic journals tend to show higher citation potentials than applied or clinical journals, and journals covering emerging topics higher than periodicals in classical subjects or more general journals. SNIP corrects for such differences. Its strengths and limitations are critically discussed, and suggestions are made for further research. All empirical results are derived from Elsevier's Scopus.