Journal Impact Factor

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The impact factor for scientific journals is released around June every year by Thomson Reuters, the guru of scientific publication metrics. All science journal editors wait for the new impact factor every year and if you are a publishing scientist you might have seen emails from at least some of the journals bragging on the improved impact factor. 

The journals with higher impact factors are considered to be more important than those with lower ones. Even some NIH grant reviewers comment on the impact factor of the scientific journals where the grant applicant publishes, to weigh in productivity and significance of past research, though whether it is a good grant review practice or not may be debatable.

Impact factor, though imperfect, is the only way to find how well a scientific journal is accepted by the peers in the area of expertise.  Impact factors are calculated yearly for those journals that are indexed in Thomson Reuters’ Journal Citation Report. In calculating the impact factor, Thomson Reuters considers not only the number of times each published paper is cited, but also the number of articles published by the journal over the year. 

According the Thomson Reuters website, “The Journal Citation Report provides quantitative tools for ranking, evaluating, categorizing, and comparing journals. The impact factor is one of these; it is a measure of the frequency with which the "average article" in a journal has been cited in a particular year or period."  For example, the number of citations during 2010 will be counted for papers published in that journal in the years 2008 and 2009.

Impact factor for a journal for 2010 is calculated by the formula: M/N, where,
M = number of times articles published in 2008 and 2009 were cited in 2010 and N = the total number of papers published by that journal during 2008 and 2009. This means that the impact factor for 2010 will be available only in 2011;  in fact they have just been published at the end of June, 2011. 

Is there a way to engineer the impact factor? The first and foremost is to publish worthy articles that will generate most citations.  But there are some aspects that editors can leverage too. An editor may suggest to authors that they actively cite papers published in that journal.  When a paper is accepted in the journal, expect the author to include citations of relevant papers published in that journal. This is considered “self-cite.” Another possible technique is that an editor may include a review article in every issue of his/her journal, reviewing all the articles appearing in that issue, with citations to each.  This is also self-cite.  Self-cites are included in the overall impact factor calculation, though they are also analyzed separately. 

It is debatable as to what extent self-citation is a fair practice. Excessive self-citation can result in removal from the index. Due to the significant effect of self-citations on their impact factors, metrics for a number of titles were not published in the 2010 Journal Citation Report.  For a list of journals removed from the Report in 2010 click here. Another way is to cut down the number of papers published in each issue, thereby shrinking the denominator in the ratio and increasing the impact factor. Lastly, there is a viral citation category of articles, which are reviews. Reviews are cited more often than original articles, so some may push for publishing one or more good reviews regularly.

Impact Factor, the Yardstick for Publishers and Scientists - ‘Black Hat’ and ‘White Hat’ Methods

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<a href="">Journal Impact Factors 2011 Release</a> published in <a href=""></a> published on June 30, 2011.

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