The extent and causes of academic text recycling or 'self-plagiarism'

Among the various forms of academic misconduct, text recycling or self-plagiarism holds a particularly contentious position as a new way to game the reward system of science. A recent case of alleged 'self-plagiarism' by the prominent Dutch economist Peter Nijkamp has attracted much public and regulatory attention in the Netherlands. During the Nijkamp controversy, it became evident that many questions around text recycling have only partly been answered and that much uncertainty still exists. While the conditions of fair text reuse have been specified more clearly in the wake of this case, the extent and causes of problematic text recycling remain unclear. In this study, we investigated the extent of problematic text recycling in order to obtain understanding of its occurrence in four research areas: biochemistry & molecular biology, economics, history and psychology. We also investigated some potential reasons and motives for authors to recycle their text, by testing current hypotheses in scholarly literature regarding the causes of text recycling. To this end, an analysis was performed on 922 journal articles, using the Turnitin plagiarism detection software, followed by close manual interpretation of the results. We observed considerable levels of problematic text recycling, particularly in economics and psychology, while it became clear that the extent of text recycling varies substantially between research fields. In addition, we found evidence that more productive authors are more likely to recycle their papers. In addition, the analysis provides insight into the influence of the number of authors and the existence of editorial policies on the occurrence of problematic text recycling.