Editorial pubs.acs.org/JPCL
Journal Impact Factor and the Real Impact of Your Paper
E
papers, measures the worldwide size of the scientific enterprise in that discipline. So, one needs to consider the individual discipline and the topics covered in each journal when comparing the JIF between two or more journals. It may be interesting to note that the majority of journals that carry very high impact factors (>25) publish just a few selected papers (100−200) each year, thus making the paper selection subjective for the editorial screening process. In addition to the two-year JIF, JCR also publishes JIFs based on a five-year analysis. The five-year JIF is a better metric because it provides a paper’s long-term impact. JCR also calculates JIFs that exclude self-citations. Typically, a journal with a lower fraction of self-citations (3−15%) reflects a broader outreach of the journal. However, for some journals this fraction remains large (>25%), thus pointing out a closely knit author network within the discipline. Any large fraction of self-citations raises a flag and leads to further investigation to determine whether the number of citations are being artificially inflated. (Note: 39 Journal titles were suppressed in 2015 by JCR because of excessive self-citations. See http://ipsciencehelp.thomsonreuters.com/incitesLive/JCRGroup/ titleSuppressions.html.) Why One Should Not Equate the Impact Factor of the Journal to the Impact of the Published Paper. The 2014 journal impact factor (JIF) list has now been released (Table 1) and journals and authors make use of this metric to promote their causes. The JIF is intended to gauge the overall impact of the journal, and one needs to scrutinize it carefully to evaluate the impact of a particular paper published in that journal. It is important to note nearly 60% of the papers published in any given journal are cited less than the average citation per paper published during the two-year JIF period. Often, review articles and a few key research papers bring in a disproportionately high number of citations to their respective journals (see the impact of the top 1% of articles in Table 1).
ach year in June, Thomson Reuters releases new journal impact factors (JIF) for scientific journals, based on the citation analysis of Journal Citation Reports (JCR). The original intent of JIF was to assist librarians in making journal selections. However, the journal impact factor has in recent years taken a prime spot in the academic and scientific worlds to judge the merit of individual publications (see 1 in Related Readings). In many countries, this metric is used to gauge the quality of published papers and commend the authors with rewards. Do the decision-making administrators consider the elements that determine the JIF? Do they evaluate the individual papers to see whether the JIF reflects the actual impact of contributed work? What Elements Determine the Impact Factor? JIF is a citation metric determined using the JCR database of Thomson Reuters. The JIF is the ratio of the number of citations in a given year to the number of papers published during the previous two years (eq 1) JIFYear YY =
(citations to research and review articles and editorials)Year YY (number of research and review articles)Years(YY‐1&YY‐2)
(1)
The JIF becomes larger with either increasing the number of citations (larger numerator) or having fewer published papers (smaller denominator). Because JIF takes into account papers published during the previous two years, it reflects a short-term impact. There have been several critical reports pointing out shortfalls in relating research performance to journal impact factor (see, for example, Related Readings 1−4). However, the JIF seems to be growing in importance among authors. A few key points that provide insight into the JIF will be discussed here. Why a Comparison of Impact Factors between Two Disciplines Is Diff icult. First of all, the JIF is highly dependent upon the discipline or field of research. Journals that exclusively publish papers related to popular topics (e.g., nanoscience, materials, and energy conversion and storage) are likely to see a greater JIF compared to journals in the broader disciplines (e.g., physical chemistry, chemical physics, condensed matter physics, mathematics). Even for popular journals, a few selected topics bring in more citations than other areas. Increased funding by government agencies for specific research topics is another factor that attracts more researchers to a specific field and, thus, increases the probability of even more papers being published in that discipline.
It is important to note nearly 60% of the papers published in any given journal are cited less than the average citation per paper published during the twoyear JIF period.
Popular topics covered through editorial matter (nonpeer reviewed articles) can also bring an increased number of citations. Citations received through editorial matter is a bonus for JIF consideration as it adds to the numerator of the JIF equation, but not the denominator. Although not a common occurrence, a few retracted papers actually continue to get citations even after the work is proved to be wrong or fraudulent. Hence, one needs to take into account all these
The JIF is highly dependent upon the discipline or field of research. There are also significant differences in impact factors depending on whether the field of research is or is not supported in large countries such as China, as citations to papers in, say, ACS journals that are in local or regional journals including foreign language journals count in the JIF. In this respect, the JIF of a given discipline, when summed over all © 2015 American Chemical Society
Published: August 6, 2015 3074
DOI: 10.1021/acs.jpclett.5b01527 J. Phys. Chem. Lett. 2015, 6, 3074−3075
The Journal of Physical Chemistry Letters
Editorial
Table 1. Comparison of 2014 Citation Metrics of Few Selected Journals that Publish Communication Type Articlesa 2014 Impact Factor (JIF) journal J. Phys Chem. Lett. Phys. Rev. Lett. Chem. Commun. Nature Commun. Chem. Phys. Lett. Appl. Phys. Lett. Phys. Chem. Chem. Phys.b ChemPhysChemb J. Chem. Phys.b Angew. Chem., Int. Ed.b
2012−2013 papers
2014 citations
2014 self-cites
2-year
2-year (without self-cites)
5-year
impact of top 1% papers (cites/paper)c
1309 7344 6309 2297 1874 10339 4069
9762 55165 43113 26346 3555 34135 18282
576 4491 3348 855 254 4970 1646
(5.90%) (8.14%) (7.77%) (3.25%) (7.15%) (14.56%) (9.00%)
7.458 7.512 6.834 11.470 1.897 3.302 4.493
7.017 6.900 6.302 11.097 1.761 2.820 4.088
7.536 7.360 6.779 11.904 1.963 3.569 4.219
84 75 51 105 14 25 37
943 5263 4564
3224 15537 51395
121 (3.75%) 4139 (26.64%) 3758 (7.31%)
3.419 2.952 11.261
3.290 2.165 10.437
3.243 3.017 12.060
32 23 99
number of papers with no citations in 2014c 74 385 410 83 563 1981 503
(5.7%) (5.2%) (6.5%) (3.6%) (30.0%) (10.7%) (12.4%)
163 (17.1%) 1131 (21.4%) 138 (3.0%)
a
Source: 2015 Journal Citation Reports and Web of Science Core Collection (Thomson Reuters, 2015). bOnly a fraction of the published articles are communication-type articles. cFrom Web of Science Core Collection, Thomson Reuters, 2015. (Document types = Articles, Reviews, Letters.)
factors while evaluating a journal’s merit as well as the impact of each particular published work. (For a humorous parody of the factors influencing impact factor, see http://www.phdcomics. com/comics/archive.php?comicid=1108.)
The impact metric of individual authors or published work is a better approach to assess the research performance than relating his/her published work to journal metrics.
The newly released 2014 impact factor of J. Phys. Chem. Lett. now stands at 7.458.
■
The newly released 2014 impact factor of J. Phys. Chem. Lett. now stands at 7.458. Does this mean all the papers published in J. Phys. Chem. Lett. from 2012 to 2013 carry a citation of 7 in 2014? The answer is obviously a “no.” Only about 40% of published papers carry an average citation equal to or more than 7.458. It is also interesting to note that 5.7% of JPCL papers failed to garner a single citation in 2014! Similar fractions of uncited papers are also found for other journals. (See Table 1 for the number of 2012−13 papers with no citations in 2014.) Clearly, one cannot judge the impact of any given paper based solely on the JIF of the journal in which it is published. The impact formula that is applied to journals can also be applied to individual authors by determining the number of citations (excluding self-citations) for papers published during the previous two years. For example, if an author publishes 20 peer-reviewed papers in two successive years and receives 100 citations (excluding self-citations) for those same papers in the following year, the impact factor of his/her published work is 5. Thus, the ratio of the citations to the number of published papers should give a measure of the impact of the individual author’s published work. Perhaps this measure of impact may serve as a better metric when evaluating the impact of an individual author’s research contributions. The impact metric of individual authors or published work is a better approach to assess the research performance than relating his/her published work to journal metrics.
AUTHOR INFORMATION
Notes
Views expressed in this Editorial are those of the authors and not necessarily the views of the ACS.
■
RELATED READINGS
(1) Van Noorden, R. Transparency Promised for Vilified Impact Factor. Nature 2014, DOI: 10.1038/nature.2014.15642. (2) Beall, J. The “Metric” System: Yet More Chaos in Scholarly Publishing. J. Phys. Chem. Lett. 2015, 6, 2020−2021. (3) Buriak, J. M. The Impact of the Impact Factor. Chem. Mater. 2014, 26, 3871−3872. (4) Van Noorden R. Scientists Join Journal Editors to Fight ImpactFactor Abuse. Nature 2013 http://blogs.nature.com/news/2013/05/ scientists-join-journal-editors-to-fight-impact-factor-abuse.html.
Prashant V. Kamat, Deputy Editor
University of Notre Dame, Notre Dame, Indiana 46556, United States
George C. Schatz, Editor-in-Chief
Northwestern University, Evanston, Illinois 60208, United States 3075
DOI: 10.1021/acs.jpclett.5b01527 J. Phys. Chem. Lett. 2015, 6, 3074−3075
