Journal impact

Researchers and publishers keep an eye on the annual impact factor of journals. The impact factor for a year is the number of current year citations of articles published in the 2 previous years divided by the total number of articles published in the 2 previous years. For example, if in 2016 there were 400 citations of articles that were published in Journal X in 2014 and 2015 and the total number of articles published by Journal X in 2014 and 2015 was 200, the impact factor for 2016 would be 400 divided by 200 = 2.0. On average, the articles published 1 or 2 years ago were cited 2 times in the 1-year time frame. This could be achieved if 1 article was cited 400 times and the remaining 199 articles were never cited, or if each article had been cited 2 times. Typically, there is a skewed distribution of citations (1,2): “The so-called 80/20 phenomenon applies, in that 20% of articles may account for 80% of the citations” (2).

There is also a 5-year impact factor that tends to suffer less year-to-year variation. The 5-year journal impact factor is the number of previous 5-year citations in the year divided by the total number of articles published in the preceding 5 years.

The impact factor is all about usage of published articles by researchers. It does not take into account the impact clinician researchers make through translation of their articles into improved clinical practice.

Dr. Eugene Garfield (1,3), one of the creators of the journal impact factor has warned that “the impact factor should not be used without careful attention to the many phenomena that influence citation rates…” He notes, for example, that “no effort is made to differentiate clinical vs laboratory studies or, for that matter, practice-based vs research based articles.” He goes on to point out that inclusion of review articles can affect the impact factor because these articles are often used in place of earlier literature and are usually cited more frequently than are research articles. Not surprisingly, journals that publish reviews only are among those with the highest impact factors. He notes, however, that mediocre review papers are not likely to improve a journal’s impact factor (3).

Currency and accessibility of articles to researchers may also influence impact factor. If an article is delayed for too long in the refereeing/processing stages it will be less current when it does appear and also may lose out in citations to related articles that were published while it was being processed. In this regard, online only journals that provide open access to everyone within days or weeks of accepting an article have an advantage over print journals.

Other factors that influence the likelihood of an article being cited in a research journal include quality of research, area of research (popular areas are more likely to be cited than areas with a small research following), local/international relevance (articles that relate specifically to a country or region are less likely to be cited widely than articles with a broader relevance), reputation of the authors, and reputation of the journal. Case reports that describe rare conditions or procedures are candidates for low citation rates.

Unfortunately, impact factor is now being used to not only judge journals but also to evaluate authors. “The misuse of the Impact Factor has become institutionalized in the research assessment methods of many universities and national evaluation panels, leading to a perverse incentive system” (2). Researchers are under pressure to publish in high impact journals and we now have a system in which papers work their way down the impact factor ladder, with rejections until they find a rung of the ladder where the article is accepted. “Ultimately, the culture will only change when the institutions responsible for overseeing the assessment of researchers and those who constitute the evaluation panels take active steps to change how they assess scientists” (2). Why do we care? We care because, although the impact factor is a measure of impact on researchers and not of impact on practicing veterinarians, the impact factor influences the decisions of clinical researchers engaged in high quality research with regard to where they submit their articles.