The ongoing proliferation of nano journals.

To the Editor — In 2010 we reported that the number of nanotechnology journals had been growing steadily since the late 1990s1. We have now updated our previous survey and we find that this growth is continuing: for example, we counted a total of 161 ‘current’ (that is, known to have published issues in 2010–2011) nano journals as of 4 March 2012, compared with 142 as of 30 October 2010, and just 15 in 1997 (Supplementary Table S1). The ‘Nanoscience & Nanotechnology’ subject category of the Journal Citation Report (JCR) published by Thomson Reuters has also grown from 59 journal titles in 2009 to 64 in 2010. Moreover, the Web of Science, also published by Thomson Reuters, has increased the number of nanotechnology journals it covers. These new journals include the Journal of Nanobiotechnology and Nanoscience and Nanotechnology Letters. Recent years have also seen increased interest in the measures used to assess the quality (or influence or impact) of journals and individual journal articles, and also individual researchers (although we do not present data on individual articles or researchers in this Correspondence). The quality of an individual article is usually judged in terms of the number of citations it receives, although other measures — notably the number of downloads2 — are becoming more widely quoted. For journals, the impact factors published by Thomson Reuters are commonly used as indicators for quality: the impact factor for a journal for year X is given by the number of times articles, reviews and other content from the previous two years are cited in the Web of Science database in year X, divided by the number of articles and reviews (but not other publication types) published in the journal during the previous two years. The limitations of impact factors have been discussed widely3 and a number of credible challengers to the impact factor have emerged4: these include the SCImago Journal Rank (SJR) values, which are produced by Elsevier’s Scopus and powered by Google’s PageRank algorithms. The SJR for year X is based on the number of times articles from the previous three years are cited by articles in the Scopus database in year X (ref. 5). However, although the impact factor calculation assigns all citations a value of 1, the SJR calculation weights each citation based on a ‘prestige’ value for the citing journal: it also stops counting ‘self-citations’ (articles in journal Y being cited by other articles in journal Y) once they reach a maximum of 1/3 of all citations received. But how different are these new measures of journal quality? The five subject categories in the JCR with the highest percentage of records retrieved by a recent nanotech search query6 included 523 journals in 2010, and SJR values are available for 499 of these. Figure 1 shows that the 2010 impact factors and the SJR values for these 499 titles are very well correlated. However, SJR values do vary among journals with the same impact factor: for example, journals with impact factors around 2.10 have SJR values in the range 0.05–0.25. (The five JCR subject categories with the highest percentages of nanotechnology articles were: Chemistry, Multidisciplinary; Chemistry, Physical; Materials Science, Multidisciplinary; Nanoscience & Nanotechnology; and Physics, Applied.) Next we consider the aggregate impact factors, which can be considered as a sort of average impact factor for a group of journals. The aggregate impact factor for year X for a subject category in the JCR is given by the number of times articles from the previous two years are cited in year X, divided by the number of articles published in that subject category during the previous two years. The aggregate impact factor of Nanoscience & Nanotechnology has been rising at a breathtaking rate compared with other subject categories. The Nanoscience & Nanotechnology subject category first appeared in the JCR in 2005, and it was ranked 53rd of the 171 subject categories in terms of aggregate impact factor. It was ranked 49th in 2006 and 50th in 2007, but then it started to rise up the rankings — to 33rd in 2008 and 22nd in 2009, and by 2010 it was ranked 13th of 174 categories. Extrapolating this growth suggests that Nanoscience & Nanotechnology may break into the top 10 in 2011. Figure 2a shows how the aggregate impact factors of 12 subject categories have changed since 2005. The subject categories are the seven subject categories The ongoing proliferation of nano journals