Impact factors of forensic science and toxicology journals: what do the numbers really mean?
Introduction
Spreading information to colleagues working in other laboratories or countries and sharing new knowledge by timely publication of research findings or providing details of new method development is fundamental for the advancement and practice of science [1]. Some have said that science does not exist until it is published [2]. The first scientific journal appeared in 1665 (The Philosophical Transactions) and the refereeing of manuscript began in 1752, when the Royal Society of London took over responsibility for this publication [3], [4]. Thousands of scientific journals are now available and many of these have wide circulation and a solid reputation for scholarly excellence. Indeed, a large proportion of manuscripts submitted to these premier journals are rejected because of shortage of space despite receiving favorable peer-review reports from the referees [5], [6]. By contrast, other periodicals have relatively small circulation numbers and some have gained a dubious reputation and seemingly publish every article submitted to them. Those persistent enough will eventually get their work published.
Besides the prestigious multidisciplinary weekly journals (Science and Nature), where only a select few manage to get their articles published, there are hundreds of specialized journals covering all branches of the pure, applied and biomedical sciences as well as the social sciences. Some journals are controlled, edited and published by scientific or professional societies and the membership is encouraged to submit their work for peer-review evaluation and possibly publication [1], [2]. With such a wide selection of journals available for submitting a manuscript, does it really matter where a paper eventually gets published?
The prestige and standing of a particular scientific journal depends on many factors including the reputation of the editor and the editorial standards, the speed of handling manuscripts, the timeliness of publication, the size of the circulation, the potential for on-line search and retrieval, and not least the rigor of the peer-review process [6]. More recently, the journal impact factor (IF) has emerged as an alternative index of quality and prestige and IFs are being used increasingly for ranking and evaluating journals and also as surrogates for judging academic performance and the quality and importance of an individual researcher’s publications [7], [8], [9], [10], [11], [12]. As impact factors are numbers reported with three decimal digits this gives them a mark of quantitative importance and prestige and they are being increasingly used by funding agencies and university search committees to evaluate individual scientists or entire departments [13], [14]. Getting articles published in journals with high impact factor is a major goal for many scientists and the way a journal’s IF fluctuates is closely monitored by publishers, editors, administrators and also by those who submit articles for publication [15]. When evaluating the productivity and scientific output of a university department, when allocating funding for research or when judging candidates for academic promotion, journal impact factors are being increasingly scrutinized [14], [15], [16], [17].
Detailed lists of journal citations and impact factors are produced and made available by the Institute for Scientific Information (ISI), which has its head offices in Philadelphia, PA. A listing of all the impact factors is included in Journal Citation Reports (JCR) and, since 1997, this product has been searchable on-line and this was the source of the data used to prepare the present review.
The impact factor of a scientific journal in a particular year is the ratio of the number of current year citations to articles published in the journal in the two preceding years divided by the number of citable items (articles and reviews) published in the same 2 years [18], [19]. For example, the 2001 impact factor for Forensic Science International (FSI) is the number of citations received by this journal in 2001 to articles published in FSI in 2000 and 1999 divided by the number of articles published in these same 2 years. Impact factors are, therefore, derived from a breakdown of the reference lists attached to the end of each article. This entails counting the number of times a particular target journal’s articles are cited as a function of the year these articles appeared in print.
One important underlying assumption of citation analysis is that citing a particular author’s work establishes a scholarly link or influence on one’s own research work [18], [19]. Journal impact factors range from 0 for the least cited journal to over 40 for some of the most highly cited journals. The median impact factor for all science journals in the ISI database for the year 2001 was about 0.80. In a relatively small discipline such as forensic and legal medicine, the impact factors of the journals are generally lower compared with broader subject categories, such as life sciences, clinical medicine and much lower than hot research topics like genetics and molecular biology [18], [19].
The aim of this article is to review and comment upon the impact factors for certain forensic science, legal medicine and toxicology journals. Many of the variables that influence the calculation of journal impact factors are discussed and some problems and pitfalls are highlighted when impact factors are used to judge the importance of the work of individual scientists.
Section snippets
Trends in impact factors of forensic science and toxicology journals
Table 1 shows the year-by-year changes (1997–2001) in journal impact factors for selected forensic science, legal medicine and toxicology journals. On the whole, impact factors of these specialist forensic science and toxicology journals changed very little over this time period [20]. The toxicology journals seemed to achieve higher impact factors than the forensic and legal medicine journals. Compared with other disciplines covered by ISI, the impact factors shown in Table 1 are relatively low
Subject categories
The Journal Citation Reports is subdivided into different subject categories. The forensic science journals are found within the subcategory “medicine, legal” and make-up a small group of only eight journals (median IF 0.96, in 2001). Moreover, some of the titles included in the list are seemingly not of any direct interest or relevance to mainstream forensic scientists, e.g. Regulatory Toxicology Pharmacology and Expert Opinion Therapeutic Patents. However, one journal that should have been
Citing and cited journal pages
The starting point for compiling journal citation reports and calculating impact factors is the reference lists or bibliographies that appear at the end of each published article in the thousands of journals covered by ISI. For example, reference lists from every article and review paper published in Forensic Science International in 2001 are scrutinized and used to find the total number of references cited. The average citation density is derived by dividing the number of references by the
Adjusting for self-citations
Research workers who publish regularly often cite their own previously published work and also articles by their colleagues who are active in similar branches of research. This is only natural considering scientists tend to build or expand on their earlier research work covering a particular area of interest. An article by one or more authors containing a bibliographic reference to earlier articles by one or more of the same authors is called a self-citation. Such self-citations usually
Long-term versus short-term impact
Some of the critics of journal impact factors maintain that a major flaw is the way that ISI makes the calculations, namely by only considering the citations to articles published in the two previous years. This method is thought to be unfair to slower moving disciplines such as Forensic Science and Toxicology as well as others. However, it is fairly easy to calculate 5- or even 10-year impact factors if considered necessary. The 5-year IF is derived by looking at all current year citations
Citation density and inclusion of review articles
Other things that are considered to influence journal impact factor and complicate comparisons between journals are the citation density and the number of review articles published each year. Citation density is the ratio of total number of references in all the articles published in a particular journal divided by the number of articles. Not many journals set limits on the number of reference items (citations) an author is permitted to include in the manuscript submitted for publication.
Concluding remarks
For some people journal impact factors have become the Holy Grail of scientific publishing [25], [26], whereas, others consider them highly contentious with many artifacts including strong national biases [27], [28], [29], [30]. This criticism is especially justified when IFs are used to evaluate and compare the productivity and importance of the work of individual scientists [31], [32], [33], [34]. There is a low correlation between the impact factor of a journal where an article is published
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