Definition of "impact."
The impact of scientific research should be assessed through more than just metrics such as Journal Impact Factor. Credit: Nick Southall (CC BY-NC 2.0)

The 2016 Journal Impact Factors (JIFs) have just been released by Clarivate (formerly part of Thomson Reuters) and are listed for the AGU journals below alongside other metrics. The Impact Factor is calculated as the ratio of citations in one year to research articles (other types of content such as editorials and commentaries are not counted) published by a journal in the previous two years.

Much has been written about the use and abuse of these data as a measure of journal quality as well as the quality of individual scholars (see here for several references). When utilizing these numbers, it is essential to understand the uncertainty around them, including whether differences between journals are significant or not. Unfortunately, the JIFs continue to be released without such contextual information.

It is well known that the final JIF for a journal is typically weighted by a few highly cited papers and when those papers are published: Papers published early in the 2-year citation window have much more of an influence on the JIF than those published later because they will have had more time to be cited in subsequent work (and some journals manipulate this). These and other factors, including differences in journal size and scope, can produce a high level of year-to-year randomness in the impact factors, even for larger journals. A recent editorial in Water Resources Research provides further discussion and analysis of these and other effects and some estimate of the minimum uncertainty across journals in hydrology.

Clarivate releases the JIF to three decimal points, but the true uncertainty makes this level of precision ridiculous and unscholarly. At least for the Earth and space sciences, the fine distinctions in rankings within a discipline provided by Clarivate, which are idiosyncratic in themselves, are likely meaningless. These biases persist even in some of the longer-term metrics and also in citation distributions. As the JIF is a metric for journals, using the JIF to assess the merit of any one paper published in a journal is simply irresponsible.

This year, for the first time, separate JIFs have been calculated by Clarivate for each Journal of Geophysical Research title. These journals received individual ISSNs in 2013 and were then considered as separate journals. Comparisons across earlier years are thus to the weighted average (by amount of content) of the entire JGR collection. A further uncertainty in this respect is that Clarivate indicated that some citations only to Journal of Geophysical Research could not be accurately assigned to a specific title thus were omitted from the JIF calculation (citation error is a concern for all titles and usually results in some undercounting). Thus, the actual JIF is likely higher by a few percentage points. We encourage researchers and journals to cite the full journal title and include the DOI of any article.

The JIF tends to get the most attention, but it is just one metric that focuses on short-term citation. Other metrics — such as the 5-Year Journal Impact Factor, Immediacy Index, Cited Half-life (all Clarivate metrics), as well as the h-index, Eigenfactor, and usage — can be used to gain a more complete view of a journal’s influence on a scientific field, although these are still influenced by a journal’s size and scope. AGU journals will soon be providing these additional metrics to provide better context.

Aside from metrics, it’s more important to look at other ways in which journals are supporting integrity around scholarly publishing and to consider this when deciding where to submit manuscripts. Read more about this in a recent Eos opinion piece.

—Brooks Hanson, Senior Vice President, Publications, AGU; email:


Hanson, B. (2017), Journal impact factors with uncertainties, Eos, 98, Published on 20 June 2017.

Text © 2017. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.