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Matthew Geiselmann is a third-year medical student at NYIT College of Osteopathic Medicine and the research coordinator at Fusion Medical Education BioSkills Lab in Hicksville, NY. Matthew’s primary interest is in Orthopedic Surgery. Adam D. Bitterman, DO is a board-certified orthopedic surgeon and an Assistant Professor of Orthopaedic Surgery at the Donald and Barbara Zucker School of Medicine at Hofstra/Northwell. He is a fellowship-trained foot and ankle specialist.
What are journal impact factors?
Though impact factors are the oldest and best-known measure of journal metrics, there is much confusion amongst medical students and residents surrounding impact factors and what these values really mean. While the impact factor rating is commonly used as a measure of importance a journal is to its academic field of interest, the method of calculation, utility, and significance are widely misunderstood. Common misconceptions surrounding impact factors are that they are a reflection of a journal’s quality of peer review process, caliber of reported content or significance of findings (1). What the impact factor really indicates is a measure that reflects the average number of citations to articles published in books, journals, conference/seminar proceedings etc. in recent years. Impact factors are applied to journals, not to individual authors, metrics like “H-Index” and “citation impact” are used when referring to an individual author. Fundamentally, impact factors can be simplified to “how frequently has this journal been cited in recent years?”. Essentially, the journal with the highest impact factor published the most commonly cited articles over the past few years (2).
Impact Factor Origin and Calculation
While the impact factor is widely used by the medical and scientific community at large, many are unaware of where it originated or how it is calculated. The idea of the impact factor was developed by Eugene Garfield, the founder of the Institute for Scientific Information (1). The concept of impact factors came out of a realization Garfield had when he was creating the Science Citation Index, an organized collection of the world’s top journals in each of their subject categories. He realized that including only the larger journals in the index would not provide the proper breadth and depth of the field’s top literature. He concluded that sorting journals by what he called “impact factor”, or average number of citations, rather than by number of articles published allows for the inclusion of many smaller but influential journals and provided a more accurate representation of the field’s important literature (3). Calculation of a journal’s impact factor is rather simple; you take the number of citations in the current year to items published in the previous 2 years and divide that by the number of articles and reviews published in the same 2 years. Let's look at the example below: take Journal “X”:
Cites in 2019 to items published in:
Number of Items Published in:
Calculation: IF 2019 = (Citations 2018 + Citations 2017) / (Publications 2018 + Publications 2017)
Impact Factor: 6.125
The calculation typically uses the previous 2 years as a standard time frame, one year could be used in rapidly changing fields. The longer the time frame used in the calculation, the less accurate the impact factor is as a representative metric of the field today (3).
Significance of Impact Factor
It is important to remember, while impact factors do tend to have a correlation with journal reliability or prestige, the metric is not inherently an indicator of journal quality. Think back to the calculation discussed earlier, the impact factor is just the ratio between citations and recent citable items published. Many academics and institutions erroneously refer to impact factors as a measure of journal quality when really it is more of a measure of influence on the academic community of interest. In reality the absolute value of a journal’s impact factor is meaningless, these values must be interpreted in the proper context (4). Citation habits and publication frequency vary widely across research fields, therefore impact factors should not be used to compare journals across disciplines (4). For instance, citation and publication frequency is much lower in math and physics than in medicine, thus medical journals will typically have higher impact factors (4,5). Review articles in particular tend to be read and cited more frequently, therefore journals that publish review articles can inflate impact factor scores (2,6). Every year editors are under pressure to increase journal impact factors. There have been instances where journal editors unethically manipulate impact factors to boost ratings for secondary gain. Editors can do this by rejecting manuscripts if they are unlikely to be frequently cited or even some have gone as far as rejecting manuscripts and strong-arming authors to cite more articles from their journal exclusively in order to be accepted (6,7). Journals with a narrow focus that cater to a more niche community such as Diagnostic Molecular Pathology will inevitably have a lower impact factor than one that reaches a broader reader base such as the Journal of Pathology (4).
The types of articles and size of the target audience a journal caters to plays an important role in the ultimate value of the impact factor. While journal impact factors can be a useful tool when evaluating and comparing journals within a particular discipline, the decision to submit your manuscript to a journal should not be entirely based on their impact factor. Know your target audience and do some digging to determine where your work would be best suited for publication and don't get too bogged down with where your publication will fall on the “prestige” rankings. For medical students and residents, the goal would be to write an article with a high impact factor. However, you generally have to walk before you run. As a result, working with an attending and publishing review articles, book chapters, and case reports is a good way to learn the basics of publishing. At this level, any publication is impressive on your curriculum vitae, and gives residency and fellowship program directors an appreciation for your ability to write well and work ethic. As your experience increases, advancing to research articles in journals with high impact factors will be an easier "next step" if you have gained some experience.
- Sharma M, Sarin A, Gupta P, Sachdeva S, Desai AV. Journal impact factor: its use, significance and limitations. World J Nucl Med. 2014;13(2):146. doi:10.4103/1450-1147.139151
- Expert Insights, 2019. The impact factor and other measures of journal prestige. [online] Wolterskluwer.com. Available at: <https://www.wolterskluwer.com/en/expert-insights/authors-impact-factor> [Accessed 14 March 2021].
- Podlubny I (2005). Comparison of scientific impact expressed by the number of citations in different fields of science. Scientometrics, 64(1), 95-99. doi: 10.1007/s11192-005-0240-0
- Garfield E. The history and meaning of the journal impact factor. JAMA. 2006;295(1):90-93. doi:10.1001/jama.295.1.90
- Esposito M. The impact factor: Its use, misuse, and significance. Int J Prosthet Dent. 2011;24:85.