Country over-citation ratios

There is a clear tendency for authors of scientific papers to over-cite the papers by their fellow countrymen (and countrywomen) relative to the percentage presence of their papers in world output in the same field. We investigated the Over-Citation Ratio (OCR) as a function of this percentage, and the effects of different scientific fields and publication years. For cancer research, we also compared clinical with basic research. We found that the OCR for a given percentage presence has been decreasing over the period 1980–2010, probably because of better communications. It is greater for fields of relatively more national interest (chemistry, ornithology) and less for those of international concern (astronomy, diabetes, cancer). It may also be slightly greater for basic cancer research than for clinical work. The OCR values given allow other types of citation, such as the references on clinical practice guidelines and papers featured in newspaper stories, to be put in context: are they unusually nationalistic, or typical of normal citation behaviour?