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Research Impact Metrics

Introduction

Journal Citation Reports calculates several supplemental metrics in addition to the impact factor that provide more details about how each journal is cited and used. Many of these metrics are not intended to measure the prestige or overall value of the journal to its field. Rather, they provide information on journals' citation patterns that indicate how researchers use them.

Immediacy Index

The journal immediacy index indicates how quickly articles in a journal are cited.

It measures the average number of times that articles published in a given calendar year are cited in the same year. It is designed to provide a measure for comparing journals that specialize in cutting-edge research.

The immediacy index is listed on a journal's profile page in Journal Citation Reports and can be located using the same steps as the impact factor.

Example:

A journal publishes 40 articles in 2016. Those articles are cited 25 times in 2016. The immediacy index is 25/40 = 0.625.

Cited Half-Life

A journal's cited half-life is the median age of articles published in that journal that were cited in the current year. Half the citations to the journal in the current year are to items published within the cited half-life.

If, for example, a journal has a cited half-life of 6.0 in 2016, that means that 50% of the citations it received in 2016 were to articles published within the most recent 6 years, 2011 - 2016. The remaining 50% were citations to articles published in 2010 or earlier.

The cited half-life is listed on a journal's profile page in Journal Citation Reports and can be located using the same steps as the impact factor.

Eigenfactor Metrics

Journal Citation Reports years 2007 and later includes two Eigenfactor Metrics for measuring journal influence, the Eigenfactor Score and Article Influence Score. For a detailed description, see Eigenfactor.org.

Eigenfactor Score

The Eigenfactor Score is calculated using the number of times articles from the journal that were published in the past five years were cited in the current year. However, journal self-citations are removed, and the score also considers the influence of the citing journals. The sum of the Eigenfactor Scores of all journals listed in Journal Citation Reports is 100.

Article Influence Score

The Article Influence Score is a measure of the average influence of a journal's articles five years after publication. The mean Article Influence Score is 1.00: articles from journals with higher scores have above-average influence, while those with lower scores have below-average influence.


Eigenfactor metrics are listed on a journal's profile page in Journal Citation Reports and can be located using the same steps as the impact factor.

Other JCR Metrics

Total cites. The total number of times that a journal has been cited by all journals included in the database in the JCR year.

Citations to journals listed in JCR are compiled annually from the JCR years combined database, regardless of which JCR edition lists the journal and regardless of what kind of article was cited or when the cited article was published. Each unique article-to-article link is counted as a citation.

Citations from a journal to an article previously published in the same journal are compiled in the total cites. However, some journals listed in JCR may be cited-only journals, in which case self-cites are not included.

(Adapted from InCites Journal Citation Reports Glossary.)

Self-citations. A self-citation is a reference to an article from the same journal. Self-citations can make up a significant portion of the citations a journal gives and receives each year. You can compare self-citing rates and self-cited rates to supplement your journal evaluation. (Adapted from InCites Journal Citation Reports Glossary.)

Citable items. Not all items published in a journal are counted as “citable.” “Citable items” are “substantive, scholarly items,” such as original research articles, review articles, reviews, and commentary, not news items, editorials, or other non-research material. Only “citable items” figure into the calculation of the Journal Impact Factor. (See McVeigh & Mann, 2009.)

% Articles in citable items. The metric “% of Articles in Citable Items” indicates the extent to which a journal focuses on original research by calculating the percentage of articles that count toward the total Citable Items. For example, in 2013, Nature has 829 articles and 28 reviews, for a total Citable Items of 857. This means that 96% of the Citable Items are original research. (Adapted from InCItes Journal Citation Reports Glossary.)

Citing half-life is the median age of articles cited by the journal in the JCR year. (From InCites Journal Citation Reports Glossary.) Not to be confused with Cited Half-Life, which refers to the age of citations to this journal.

Article influence score. The Article Influence Score determines the average influence of a journal's articles over the first five years after publication.  It is calculated by multiplying the Eigenfactor Score by 0.01 and dividing by the number of articles in the journal, normalized as a fraction of all articles in all publications.  This measure is roughly analogous to the 5-Year Journal Impact Factor in that it is a ratio of a journal’s citation influence to the size of the journal’s article contribution over a period of five years. 

The mean Article Influence Score for each article is 1.00. A score greater than 1.00 indicates that each article in the journal has above-average influence. A score less than 1.00 indicates that each article in the journal has below-average influence.

(From InCites Journal Citation Reports Glossary.)

Normalized eigenfactor. The Normalized Eigenfactor Score is the Eigenfactor score normalized by rescaling the total number of journals in the JCR each year, so that the average journal has a score of 1. Journals can then be compared and influence measured by their score relative to 1. For example, if a journal has a Normalized Eigenfactor Score of 5, that journal is considered to be 5 times as influential as the average journal in the JCR. (From InCItes Journal Citation Reports Glossary.)