In a striking case of the experts falling foul of a phenomenon studied by themselves and their colleagues - the self-serving bias - it turns out that psychologists have a tendency to over-cite their own research papers.
Marc Brysbaert and Sinead Smyth analysed one recent issue of Psychological Science and the Journal of Experimental Psychology: Learning, Memory, and Cognition and two recent issues of the Quarterly Journal of Experimental Psychology and the European Journal of Cognitive Psychology.
For each of the articles in these journals, Brysbaert and Smyth used the 'find related records' function on the ISI Web of Science to find the article out there in the wider literature with the greatest overlap in the references it cited, but which was written by a different set of authors. This way the researchers ended up with a list of original target articles, each one paired with a second comparison paper by a different research group, presumably on the same or a highly similar topic (hence the overlap in the reference lists).
To check for a self-citation bias, Brysbaert and Smyth simply looked to see how many times the authors of a target article cited themselves compared with how many times they cited the authors of the comparison paper (and vice versa). For target articles, the average number of self-citations was 4.1 (11 per cent) compared with 2.3 citations of the comparison paper's authors. For the comparison papers, the average number of self-citations was 9 (10 per cent), compared with 1.8 citations of the authors of the target article.
The researchers summed up: 'A typical psychology article contains 3 to 9 self-citations, depending on the length of the reference list ... In contrast, cited colleagues in general receive 1 to 3 citations. This is what we call the self-citation bias: the preference researchers have to refer to their own work when they [supposedly] guide readers to the relevant literature.' The finding adds to past research that's shown academics are biased towards citing other researchers from their own country, and towards citing the work of the editor of the journal their research is published in.
Brysbaert and Smyth believe that psychology researchers indulge in biased self-citation practices not because their own past papers are always necessarily useful to the reader, but because it's 'good for the researchers' esteem, by means of self-enhancement and self-promotion.'
If that's the case, does it work? The evidence for this is mixed. A 2006 study in the field of economics found that papers with more self-citations were no more likely to end up being cited by other research groups. However, another study published in 2007 (pdf), which involved the analysis of over 64,000 Norwegian journal articles, found that authors who self-cited more also tended to receive more citations from others. 'So, although self-citations may not increase the likelihood that a particular article is cited, they do increase the chances that a particular author is cited,' Brysbaert and Smyth explained.
So, what to do about this self-citation bias? One option proposed by Brysbaert and Smyth is for journals editors to impose a cap on self-citations, particularly for journals, like Psychological Science, that have a cap on the total number of references allowed per paper - articles in this journal tended to have the highest proportion of self-citations. What do you think?
Marc Brysbaert, and Sinead Smyth (2011). Self-enhancement in scientific research: The self-citation bias, Psychologica Belgica. In Press. [pdf via author website].