Feature Article: Impact Factor

The impact factor is a measure widely adopted in academia to evaluate the standing of a journal. It was developed with the idea of discovering the most important journals in a particular research area. Eugene Garfield, who is regarded as the founder of the impact factor, developed the methodology for an indexing system for academic literature based on their citations (Garfield, 1955, 2006).

The impact factor helps one to evaluate the relative importance of a journal, in particular when one wants to compare it with others in the same field. It is a standardized measure of how often articles from the journal have been cited in other indexed journals over the previous two years. The impact factor of a journal in a given year is calculated by dividing the number of citations of articles in that journal published in the two preceding years by the total number of articles published in that journal during that period. For example, if a journal has an impact factor of 1 in 2015, it implies that its papers published in 2013 and 2014 were cited once on average in 2015. There can also be other periods of time for calculating impact factors, such as the five-year impact factor. A higher impact factor means more citations per article published in a journal over the period. This information is provided in the Journal Citation Reports by Thomson Reuters.

The impact factor is useful for authors for identifying the appropriate journal for manuscript submission. It is also important for researchers to find out the most cited journals to get research information from, as well as to compare journals within the same disciplinary field. Take the subject category ‘education & educational research’ as an example. In the year 2014, the 224 journals had impact factors ranging from 0.000 to 3.897, with a median of 0.740. It is reasonable to infer that the journals with impact factors above the median attract the more outstanding research work in the discipline.

In selecting a journal for submit manuscripts to, one might choose to select one with a high impact factor. However, publication delay may occur in high impact journals due to the high volume of submissions and the rigorous review process. Therefore, one may first consider whether the manuscript is to be submitted to a high impact journal despite the higher risk of rejection; or to a journal with a comparatively lower impact factor with potentially a higher chance of being accepted. Other considerations also play a role. If the journal is not directly related to one’s speciality, the published works might not reach and be read by target audience.

Despite the widespread use of impact factor, its limitations have been recognized. A major one is that the factor is highly dependent on the academic discipline. The impact factors themselves cannot be used to compare journals across disciplines. Despite the limitations, one should be aiming to publish in high impact journals, which in general have higher academic standing, and are more likely to attract citations.

Garfield, E. (1955). Citation indexes for science: A new dimension in documentation through association of ideas. Science, 122(3159), 108–111.

Garfield, E. (2006). The history and meaning of the journal impact factor. The Journal of the American Medical Association, 295(1), 90–93.



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