What is the impact factor?
The impact factor is a measure of citations (A) in a given year (e.g., 2011) to particular papers (B) published in the previous two years (e.g., 2009 and 2010). The impact factor is A divided by B. Excluded are contributions such as correspondence and editorials. However, it is worth noting that citations in these entities do contribute to A.
It is also worth noting that papers cited in a particular year from that year—2011 papers cited in 2011, for example—do not contribute to the impact factor. In fact, papers cited within their calendar year of publication have no effect on the impact factor. Therefore, if editors want to play the impact-factor game—legitimately—it is obvious that they must: 1) publish as many highly citeable papers as possible; 2) increase citation of them by generating comment in letters and editorials (within reason) and 3) time the publication of citing entities properly. For example, an editorial that cites a paper published in 2011 is better published in January 2012 than December 2011. It must be noted that Thompson Reuters, who “owns” the impact factor, does police the process and look for anomalous patterns of citation.
Can editors influence impact factor?
The answer is, clearly, yes. However, how long does it take an editor—say, one appointed in January 2011—to influence the impact factor of a journal, and is this a legitimate measure of editor performance? In the year of appointment, an editor has no influence on impact factor because the metrics, which are based on the previous year, are already fixed.
In the second year of appointment, the editor has minimal influence, because only one year’s worth of material published under his or her tenure may be considered for citation, and a high proportion of this is likely to have been accepted by the predecessor. However, measures taken in the second year to increase citations to the journal’s content can have an influence, but only to the extent that they reference the one year’s worth of content controlled by the new editor.
In the third year of appointment, all material published in the previous two years and some of the year preceding is the responsibility of the editor, and any measures taken to increase citations in that year are restricted to those two years.
Only in the fourth year of appointment can the editor take full responsibility for citing content and content being cited in the journal. Therefore, following appointment, it takes four years (until the end of 2015, using the present example) for an editor to significantly affect the impact factor.
If measures taken are successful, the editor is lauded and is safe in the job. If measures taken are not successful, the publisher has a dilemma: sack the editor in the knowledge that his or her successor will take four years, fully, to influence the impact factor, or continue with the same editor in the hope of improved performance.
Things usually continue with little change for a year after an editor’s contract expires and a new editor is hired. Therefore, my conclusion about impact factor is that, while it is a controversial measure of journal quality, it is a useless measure of editor performance.