Authors residing in the United States are more likely to be highly-cited if they publish their articles in British journals, especially in BMJ (Fig 1A). This would seem to support the social ties explanation. However, the reverse is not true — British authors are more likely to be poorly-cited if they publish in US journals (this effect driven mostly by JAMA).

With only 4 journals in the dataset, it would be difficult to discern journal effects from social network effects.

First, as Phil suggests, researchers based in developing countries may work on different medical problems for which there is a smaller community of researchers. This would result in a smaller universe of potential citing papers and prevent any inference on citations as indicators of quality.

Second, it could be that developing country researchers have less opportunities to make their work known and weaker social ties with their peers, which would also lead to lower citation rates.

Patrick Gaule