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Research Metrics: Measuring the Influence and Impact of Research

A guide to understanding impact factors, journal rankings, h-index, alt-metrics, and other means of analyzing the influence and impact of published research.

What is the Impact Factor?

The journal Impact Factor is the average number of times articles from the journal published in the past two years have been cited in the JCR year.

The Impact Factor is calculated by dividing the number of citations in the JCR year by the total number of articles published in the two previous years. An Impact Factor of 1.0 means that, on average, the articles published one or two year ago have been cited one time. An Impact Factor of 2.5 means that, on average, the articles published one or two year ago have been cited two and a half times. Citing articles may be from the same journal; most citing articles are from different journals.

For example, the journal PLoS Biology's 2010 impact factor is 12.472.

This was calculated thusly:

5076   - total of all citations from 2010 articles to PLoS Biology articles published in 2009 (1971) and 2008 (3105)
divided by
407    - total of PLoS Biology articles published in 2009 (195) and 2008 (212)
= 12.472

The number by itself does not mean as much. If you knew that the journal with the highest impact factor has the number 94.333, you might think 12.472 was quite low. But when you look at the impact factors of all the Biology journals indexed by JCR, PLoS Biology is ranked No. 1 in the Biology subject category.

Journal Citation Reports (JCR)

Journal Impact Factors can be found in the Thomson Reuters' resource, Journal Citation Reports (JCR).


SCImago Journal and Country Rank is a portal that includes the journals and country scientific indicators developed from the information contained in the Scopus® database.

More JCR Metrics

In addition to the Impact Factor, JCR will also include the following metrics for a journal

Cost-Effectiveness of Open Access Journals

From "Price doesn't always buy prestige in open access" - Nature News, Jan. 22. 2013

The graph above utilizes a new tool, called Cost Effectiveness for Open Access Journals It incorporates pricing and prestige information for 657 open-access journals indexed by Thomson Reuters, including 356 that do not charge any fees.The data are plotted to show a journal's Article Influence (AI) score against the fee it charges per article. The AI score is calculated by dividing the Eigenfactor Score of the journal by the number of articles in the journal, normalized so that the average journal has an AI equal to 1. Eigenfactor Scores are like impact factors in that they are based on citations, but they also take into account the source of the citations.

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