Introducing the Journal Citation Indicator: A new, field-normalized measurement of journal citation impact

This is the second in a series of updates to provide information on the launch of the 2021 Journal Citation Reports release.

In a recent blog post we discussed refinements in this year’s forthcoming release of the Journal Citation Reports (JCR)™, describing the addition of new content and hinting at a new metric for measuring the citation impact of a journal’s recent publications.

I’m now pleased to fully introduce the Journal Citation Indicator. By normalizing for different fields of research and their widely varying rates of publication and citation, the Journal Citation Indicator provides a single journal-level metric that can be easily interpreted and compared across disciplines.

The Journal Citation Indicator will be calculated for all journals in the Web of Science Core Collection™ – including those that do not have a Journal Impact Factor (JIF)™ – and published in the 2021 JCR in June.

 

“The Journal Citation Indicator provides a single journal-level metric that can be easily interpreted and compared across disciplines.”

 

Beyond mere citation counts

Citations serve as an immediate, valid marker of research influence and significance, reflecting the judgments that researchers themselves make when acknowledging important work. Nevertheless, citations must be considered carefully and in context. For validity in assessing the impact of published research, citation analysis must control for such variables as subject field, document type and year of publication.

The new Journal Citation Indicator meets this requirement for journal evaluation, providing a single number that accounts for the specific characteristics of different fields and their publications. Although the calculations behind the Journal Citation Indicator are complex, requiring considerable computing power, the end result is simple:  a single value that is easy to interpret and compare, complementing current journal metrics and further supporting responsible use.

In its calculation for a given journal, the Journal Citation Indicator harnesses another Clarivate measure: Category Normalized Citation Impact (CNCI), a metric found in the analytic and benchmarking tool InCites™. The value of the Journal Citation Indicator is the mean CNCI for all articles and reviews published in a journal in the preceding three years. (For example, for the 2020 Journal Citation Indicator value, the years under analysis are 2017, 2018 and 2019.)

As in the CNCI measurement, the Journal Citation Indicator calculation controls for different fields, document types (articles, reviews, etc.) and year of publication. The resulting number represents the relative citation impact of a given paper as the ratio of citations compared to a global baseline. A value of 1.0 represents world average, with values higher than 1.0 denoting higher-than-average citation impact (2.0 being twice the average) and lower than 1.0 indicating less than average.

In essence, the Journal Citation Indicator provides a field-normalized measure of citation impact where a value of 1.0 means that, across the journal, published papers received a number of citations equal to the average citation count in that subject category.

 

Comparing the Journal Citation Indicator and the Journal Impact Factor

The Journal Citation Indicator is designed to complement the JIF – the original and longstanding metric for journal evaluation – and other metrics currently used in the research community. In addition to the use of normalization, there are several key differences between the Journal Citation Indicator and the JIF.

For example, the Journal Citation Indicator’s calculation on three years of publications contrasts with the two-year window employed for the JIF. This three-year calculation enables the Journal Citation Indicator to be as current as possible, while also allowing more time for publications to accrue citations.

Also, the JIF calculation is based on citations made in the current year, while the Journal Citation Indicator counts citations from any time period following publication, up to the end of the current year.

The table below summarizes how the Journal Citation Indicator compares to the JIF in various measurements.

Table 1 – Comparison of Journal Citation Indicator to JIF

Feature Journal Impact Factor Journal Citation Indicator
All Web of Science Core Collection journals N Y
Field-normalized citation metric N Y
Fixed dataset Y Y
Counts citations from the entire Core Collection Y Y
Counts citations from the current year only Y N
Includes Early Access (EA) content from 2020 onward Y Y
Includes unlinked citations Y N
Fractional counting N N

 

Required: Responsible, informed interpretation

Despite the increased uniformity and comparability afforded by the Journal Citation Indicator, as with any metric, interpretation must be instilled with judgment. Closely adjacent fields – e.g. those in the physical sciences – can be compared fairly readily. On the other hand, comparing journals in physical-science fields with, say, those in the arts and humanities, would not be advisable, as publication output, citation dynamics and other elements tend to differ so sharply between those areas.

The Journal Citation Indicator will bring citation impact metrics to the full range of journals indexed in the Web of Science Core Collection, increasing the utility of the JCR as it expands its coverage to more than 21,000 scholarly publications. Providing this information for around 7,000 journals in the ESCI will increase exposure to journals from all disciplines, helping users to understand how they compare to more established sources of scholarly content. By incorporating field normalization into the calculation, the Journal Citation Indicator will also allow users to compare citation impact between disciplines more easily and fairly. When used responsibly it can support more nuanced research assessment.

The debut of the Journal Citation Indicator represents only the latest development in the long evolution of the JCR – a continuum that has recently seen the addition of Open Access data, Early Access content and more.

What’s more, the evolution continues: watch this space for details on further refinements in the new release that will transform the JCR user experience.

 

Read the full white paper  for a detailed discussion of the Journal Citation Indicator, its calculation and its implications.

Find out more about the Journal Citation Reports here.