Geometric journal impact factors correcting for individual highly cited articles

TL;DR

This study demonstrates that using the geometric mean instead of the arithmetic mean in journal impact factors reduces their sensitivity to highly cited articles, leading to more stable journal rankings over time, with Mendeley readership data providing comparable stability.

Contribution

It introduces the use of the geometric mean for calculating impact factors and compares its stability with traditional methods and alternative impact indicators.

Findings

Geometric mean-based impact factors are more stable over time.

Mendeley readership impact factors are as stable as citation-based ones.

Using geometric mean slightly improves the stability of journal rankings.

Abstract

Journal impact factors (JIFs) are widely used and promoted but have important limitations. In particular, JIFs can be unduly influenced by individual highly cited articles and hence are inherently unstable. A logical way to reduce the impact of individual high citation counts is to use the geometric mean rather than the standard mean in JIF calculations. Based upon journal rankings 2004-2014 in 50 sub-categories within 5 broad categories, this study shows that journal rankings based on JIF variants tend to be more stable over time if the geometric mean is used rather than the standard mean. The same is true for JIF variants using Mendeley reader counts instead of citation counts. Thus, although the difference is not large, the geometric mean is recommended instead of the arithmetic mean for future JIF calculations. In addition, Mendeley readership-based JIF variants are as stable as those using Scopus citations, confirming the value of Mendeley readership as an academic impact indicator.