Librarians and information scientists have been evaluating journals for at least 75 years. Gross and Gross conducted a classic study of citation patterns in the ’20s.1 Others, including Estelle Brodman with her studies in the ’40s of physiology journals and subsequent reviews of the process, followed this lead.2 However, the advent of the Clarivate Analytics citation indexes made it possible to do computer-compiled statistical reports not only on the output of journals but also in terms of citation frequency. And in the ’60s we invented the journal “impact factor.” After using journal statistical data in-house to compile the Science Citation Index (SCI) for many years, Clarivate Analytics began to publish Journal Citation Reports (JCR)3 in 1975 as part of the SCI and the Social Sciences Citation Index (SSCI).
The JCR 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. The annual JCR impact factor is a ratio between citations and recent citable items published. Thus, the impact factor of a journal is calculated by dividing the number of current year citations to the source items published in that journal during the previous two years (see Figure 1).
The impact factor is useful in clarifying the significance of absolute (or total) citation frequencies. It eliminates some of the bias of such counts which favor large journals over small ones, or frequently issued journals over less frequently issued ones, and of older journals over newer ones. Particularly in the latter case such journals have a larger citable body of literature than smaller or younger journals. All things being equal, the larger the number of previously published articles, the more often a journal will be cited. 4, 5
There have been many innovative applications of journal impact factors. The most common involve market research for publishers and others. But, primarily, JCR provides librarians and researchers with a tool for the management of library journal collections. In market research, the impact factor provides quantitative evidence for editors and publishers for positioning their journals in relation to the competition—especially others in the same subject category, in a vertical rather than a horizontal or intradisciplinary comparison. JCR data may also serve advertisers interested in evaluating the potential of a specific journal.
Perhaps the most important and recent use of impact is in the process of academic evaluation. The impact factor can be used to provide a gross approximation of the prestige of journals in which individuals have been published. This is best done in conjunction with other considerations such as peer review, productivity, and subject specialty citation rates. As a tool for management of library journal collections, the impact factor supplies the library administrator with information about journals already in the collection and journals under consideration for acquisition. These data must also be combined with cost and circulation data to make rational decisions about purchases of journals.
The impact factor can be useful in all of these applications, provided the data are used sensibly. It is important to note that subjective methods can be used in evaluating journals as, for example, by interviews or questionnaires. In general, there is good agreement on the relative value of journals in the appropriate categories. However, the JCR makes possible the realization that many journals do not fit easily into established categories. Often, the only differentiation possible between two or three small journals of average impact is price or subjective judgments such as peer review.
Clarivate Analytics does not depend on the impact factor alone in assessing the usefulness of a journal, and neither should anyone else. The impact factor should not be used without careful attention to the many phenomena that influence citation rates, as for example the average number of references cited in the average article. The impact factor should be used with informed peer review. In the case of academic evaluation for tenure it is sometimes inappropriate to use the impact of the source journal to estimate the expected frequency of a recently published article. Again, the impact factor should be used with informed peer review. Citation frequencies for individual articles are quite varied.
Review articles generally are cited more frequently than typical research articles because they often serve as surrogates for earlier literature, especially in journals that discourage extensive bibliographies. In the JCR system any article containing more than 100 references is coded as a review. Articles in “review” sections of research or clinical journals are also coded as reviews, as are articles whose titles contain the word “review” or “overview.”
The Source Data Listing in the JCR not only provides data on the number of reviews in each journal but also provides the average number of references cited in that journal’s articles. Naturally, review journals have some of the highest impact factors. Often, the first-ranked journal in the subject category listings will be a review journal. For example, under Biochemistry, the journal topping the list is Annual Review of Biochemistry with an impact factor of 35.5 in 1992.
It is widely believed that methods articles attract more citations than other types of articles. However, this is not in fact true. Many journals devoted entirely to methods do not achieve unusual impact. But it is true that among the most cited articles in the literature there are some super classics that give this overall impression. It should be noted that the chronological limitation on the impact calculation eliminates the bias super classics might introduce. Absolute citation frequencies are biased in this way, but, on occasion, a hot paper might affect the current impact of a journal.
Different specialties exhibit different ranges of peak impact. That is why the JCR provides subject category listings. In this way, journals may be viewed in the context of their specific field. Still, a five-year impact may be more useful to some users and can be calculated by combining the statistical data available from consecutive years of the JCR (see Figure 2). It is rare to find that the ranking of a journal will change significantly within its designated category unless the journal’s influence has indeed changed.
While Clarivate Analytics does manually code each published source item, it is not feasible to code individually the 12 million references we process each year. Therefore, journal citation counts in JCR do not distinguish between letters, reviews, or original research. So, if a journal publishes a large number of letters, there will usually be a temporary increase in references to those letters. Letters to the Lancet may indeed be cited more often that letters to JAMA or vice versa, but the overall citation count recorded would not take this artifact into account. Detailed computerized article-by-article analyses or audits can be conducted to identify such artifacts.
Some of the journals listed in the JCR are not citing journals, but are cited-only journals. This is significant when comparing journals by impact factor because the self-citations from a cited-only journal are not included in its impact factor calculation. Self-citations often represent about 13% of the citations that a journal receives. The cited-only journals with impact factors in the JCR Journal Rankings and Subject Category Listing may be ceased or suspended journals, superseded titles, or journals that are covered in the science editions of Current Contents, but not a citation index.
A title change affects the impact factor for two years after the change is made. The old and new titles are not unified unless the titles are in the same position alphabetically. In the first year after the title change, the impact is not available for the new title unless the data for old and new can be unified. In the second year, the impact factor is split. The new title may rank lower than expected and the old title may rank higher than expected because only one year of source data is included in its calculation (see Figure 4). Title changes for the current year and the previous year are listed in the JCR guide.
The impact factor is a very useful tool for evaluation of journals, but it must be used discreetly. Considerations include the amount of review or other types of material published in a journal, variations between disciplines, and item-by-item impact. The journal’s status in regard to coverage in the Clarivate Analytics databases as well as the occurrence of a title change are also very important. In the next essay we will look at some examples of how to put tools for journal evaluation into use.
How to Calculate Journal Impact Factor Explained
Why is the impact factor important?
The impact factor of a journal can determine the funding, submissions and reputation of publishers and academic writers. Maintaining the quality of work being published increases the frequency or references and improves the overall ranking of the journal. Journals that boast high impact factor values appear as well-managed and prestigious publications.
What is the impact factor?
The impact factor refers to a measurement of the influence and authority of a published piece of work. Impact factor calculations can measure citations and impact for both individual authors and overall journal publications.
Personal impact factor
The personal impact factor calculates the reach and references of your publications. This measurement displays the average number of times that your personal writing appears as a reference in other works. You can calculate your personal impact factor by counting the number of citations of your work and dividing it by the total number of pieces published.
Journal impact factor
The impact factor is a value that determines the ranking and status of an academic journal. This value represents the average number of references for articles within a journal. The impact factor offers insight into the reach, quality and influence of the information provided by the publisher or journal. You can calculate the average references for various time frames and use the value to compare journals with information relating to a particular field of study.
When to use impact factor
The impact factor allows authors, students and users to analyze a visual hierarchy of the academic journals present in their field. Consulting this ranking allows you to assess which journals align with the needs and values of your writing.
Submitting an article
As an author or student, you may submit an article to be published in a journal. Assessing the rank and status of various journals can help you decide which publication has the highest rate of views and citations. Publishing an article in a well-known or high-ranking journal increases the authority and reach of your work and creates a powerful impression for future employers or recruiters.
Assessing academic success
The impact factor of a journal can serve as an indicator of a students or professionals level of success in their field. Journals with high impact factor rankings typically hold the articles that they accept and publish to a higher standard of writing or information. Having an article published in a high-ranking journal can distinguish you as a successful and skilled writer or researcher in your field.
Personal impact factor calculations can also display the importance and success of your published content. Having a high number of references and a high average impact value means that your claims and findings receive support and serve as useful for others in academic settings. A high personal impact factor establishes your credibility and knowledge of topics in your field.
How to calculate the journal impact factor
Here are three steps you can follow to calculate and rank the impact factor of an academic journal:
1. Count the number of total citations
The impact factor determines the average number of citations for the journal over two years. The total number of times that the journal received a reference represents the first value necessary to perform this calculation. Any piece that references a portion of the journal counts as a reported citation.
2. Divide by the number of citable articles
After totaling the number of references made in the specified time frame, find the average number of references per article. You can calculate this average by dividing the total number of citations by the number of citable articles within the publication. Ensure that you only account for articles that allow for references.
3. Compare to other journals
Once you have the average number of article citations, you can use this information to place the journal in a ranking system. You can order journals with similar topics and audiences by their calculated impact factor measurement. Articles with higher impact factor values convey a higher level of information and scholarly authority.
How to calculate the personal impact factor
Follow these three steps to measure the personal impact factor of your academic writing and publications:
1. Count the total citations
To calculate the average number of citations for your works, first identify and total the number of times other publications reference your pieces. Typically, this total refers to citations within a time frame of one or two years. This value represents the first portion of the impact factor calculation.
2. Divide by the number of published works
The personal impact factor calculates an average. To determine the average value, you can divide the total number of citations by the total number of articles that you published within your determined timeframe. Ensure to include only articles that allow for citations and articles that credit you as an author.
3. Compare to other authors
Once you find the average number of references for your publications, you can use the personal impact factor value to compare and rank yourself. Compare your value with the averages of other professionals or students in your field and at your level of experience. Identifying how you compare with others allows you to understand the quality and importance of your writing and allows you to display your rank to employers, recruiters and supervisors.
Is an impact factor of 2.8 good?
How are impact factors calculated manually?
- Journal Impact Factor (JIF) or Impact Factor (IF) of an academic journal is a measure, calculated by the yearly average number of citations to recent articles published in that particular journal. …
- Impact Factor(IF-2018) = A/B.
- For Example,
- Then the Impact factor of the Journal should be (1298/541)= 2.40 IF.
- For example,
How is impact number calculated?