In reply to Tomáš Opatrný's Correspondence 'Playing the system to give low-impact journals more clout' (Nature 455, 167; 2008), we would like to point out that the practice of journal self-citation is not new. Thomson Reuters is aware that some journals have used extensive reference to their prior content to influence their citation metrics. The contribution of so-called journal self-citation has been included in Journal Citation Reports since it first appeared in 1975. In recent years, these data have been made more prominent to inform our subscribers of the effects of journal self-citation.
Thomson Reuters also reviews self-citation data for journals in which an exceptionally high self-citation rate artificially influences the impact factor and therefore belies its contribution to the scientific literature. The role of a journal's impact factor as an objective and integral measure becomes questionable at this level of self-citation.
Nine journals received no listing in Journal Citation Reports last year because of exceptionally high self-citation counts; their titles are listed in the Notices file on the journal's website. Journal self-citations will be reviewed each year. Once the problem of excessive self-citation resolves and we can publish an accurate impact factor, the titles will again appear in the journal. Each title continues to be indexed in other Thomson Reuters products.
The cause of the increased 2007 impact factor of Folia Phoniatrica et Logopaedica will be examined as part of the routine review of journal self-citations, and a decision will be made regarding continued listing of the journal in 2008's Journal Citation Reports.
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Testa, J. Playing the system puts self-citation's impact under review. Nature 455, 729 (2008). https://doi.org/10.1038/455729b