Introduction to Journal Impact Factor and h-Index
Influence and relevance to contemporary scientific publishing and scholastic achievements
by Dr Chun-Yang Yin
Scientific publishing is an essential component in the dissemination of research findings to both the academic community and general public. Among scholars in contemporary academic settings, the maxim publish or perish is well-known since publications dictate the professional development of scholars and how well they will do in terms of academic promotion and attainment of tenure. The desire to publish research findings in indexed and archived journals is further augmented by the promise of financial reward or cash incentives in developing countries such as China, Malaysia and Pakistan1.
In this day and age, scientific publishing is rendered increasingly complex due to the proliferation of journals and introduction of various research metrics meant for representation (or proxy) of academic prestige. The two most pervasive modern-day research metrics since the onset of the information age are the Journal Impact Factor (JIF, which is published by Thomson Reuters) and the h-index2. The JIF, arguably one of the most established metrics within academia, is used to evaluate the relative influence, importance or prestige of scholarly journals. It is based on two elements: the numerator (the ratio of the number of citations in the current year to the items published in the previous two years) and the denominator (the total number of articles and reviews published in the same two years)3. For example, in the form of a mathematical expression, the JIF of a journal in 2007 can be calculated as follows:
JIF of a journal in the year 2007 = X/Y
where X = the number of citations of articles (published in 2005 and 2006) received in 2007
Y = the total number of articles and reviews published in 2005 and 2006.
Even though the popularity of this metric among the scholarly community is never in doubt, it is frequently criticised for its limitations4. These limitations include bias towards journal popularity over prestige5 , its abuse by journal editors6 and insensitivity to journal self-citations7 whereby a citation can be categorised as a self-citation if any of the authors of the citing article is also an author of the cited article. The usage of JIF for absolute comparison between two journals of different fields (e.g. life sciences and engineering journals) is invalid since a prestigious life sciences journal may have a JIF more than 15 while a prestigious engineering journal may only have a JIF of about two8. This discrepancy may stem from various factors such as (1) varying citation “densities” across different disciplines (e.g. in some disciplines, the literature list of an average article is longer than in other disciplines: more citations are given and thus higher number of citations can be received within that discipline), (2) some disciplines cite recently published documents more frequently than other disciplines, and (3) used publication channels (e.g. journals, monographs, conference papers) differ per discipline9. The over-emphasis on JIF as a proxy for prestige has resulted in the shifted focus of certain academics in the abovementioned countries to publish review articles in discipline-specific journals (e.g. chemical engineering journals) with high JIFs but are rather generic and not as technically-based as good and top-notch journals in that particular discipline. This practice can be beneficial to postgraduate students attempting to gain a foothold on scholarly publishing but over-reliance on such practice to increase the number of publications and generate citations will ultimately prove detrimental to the academic credibility of the affected scholars.
Another important research metric is the h-index, although it is used to assess the scholastic impact of individuals rather than an evaluation of journal popularity. The h-index (h denotes high-impact) is originally intended to quantify an individual’s scientific research output and impact in which ‘a scientist has index h if h of his or her Np papers have at least h citations each and the other (Np – h) papers have ≤ h citations each’2. In other words, this is the highest number of papers that an individual has written that have each received at least that number of citations. The h-index of an individual can be determined by plotting a curve of his/her number of citations against paper number (Figure 1). A line from the origin can be drawn 45° from the x-axis and the intersection of this line with the curve determines the h-index. The Scopus database includes this curve as one of its features. Alternatively, one can obtain the h-index of a particular researcher by using a specific database (e.g. Scopus or Thomson Reuters Web of Knowledge SM). This can be accomplished by retrieving all published items (articles, reviews, etc.) of a particular researcher throughout his/her career and sorting them by the number of ‘‘Times Cited’’.The highest rank number which is still lower than the corresponding ‘‘Times Cited’’ value is the h-index of the researcher.
The h-index is not only used as a measure of scientific achievement for individual researchers but also to determine the scientific output of research groups10, scientific facilities and countries11. The h-index is meant to circumvent the main disadvantages of other research metrics such as total number of papers and/or citation counts. This is because the total number of papers does not indicate the quality of scientific publications whereas citation counts can be disproportionately affected by a single publication of major influence. Nonetheless, one of the main disadvantages of h-index is that the number does not decrease with time, making it biased when used to measure the impact of an individual who has been working for decades. It is therefore prudent to use the index within a stipulated citation time window (normally within a 5-year time window) when comparing the influence of researchers.
It is important for academics to use their discretion judiciously when deciphering the prestige of a particular journal based on JIF or the level of scholastic achievement of an academic based on his/her h-index. The ability to judge the impact/prestige of scientific journals can be honed by extensively reviewing published journal articles across a wide range of publishers, and not fixated on just a popular online database operated by a single publisher. In many cases, the most prestigious journals in respective scientific fields are actually published by scholarly societies and institutes rather than highly commercialised publishers. Examples of such scholarly societies include The American Chemical Society/Royal Society of Chemistry (chemistry), American Physical Society (physics), The American Society for Biochemistry and Molecular Biology (biology), Institute of Electrical and Electronics Engineers (electrical/electronics engineering) and Princeton University and the Institute for Advanced Study (mathematics). After familiarisation with the good and prestigious journals in their respective fields, the relative achievement of academics can be ascertained by scrutinising their publication list coupled with information on citation counts and h-index rather than just relying on one research metric.
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 Yin, C.Y. and Abdul-Talib, S. (2010). Writing & Publishing Peer-Reviewed Scientific Journal Articles. University Publication Centre, Universiti Teknologi MARA, Shah Alam, Malaysia, pp. 55. ISBN: 978-967-363-030-1.
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ABOUT THE AUTHOR:
Dr Chun-Yang Yin is a lecturer at the School of Chemical and Mathematical Sciences, Murdoch University, Western Australia. He has had industrial experience in the environmental engineering sector and taught at several Malaysian universities and Monash University (Malaysian campus) before joining Murdoch University as a full-time faculty member in November 2010. Dr Yin received his Ph.D. in chemical engineering from University of Malaya and has been appointed as visiting scholar at Columbia University and Harvard University. Dr Yin has published more than 40 international journal articles mostly as first/corresponding author. His current research interests are application of microfluidics in minerals extraction, synthesis of carbon microspheres and porous materials for various industrial applications and determination of ionic liquids toxicities. He can be contacted at [email protected]. Visit his Scientific Malaysian profile at http://www.scientificmalaysian.com/members/yinchunyang/