Yet another new (June 2009) Research Information Network research report, The UK’s Share of World Research Output : an investigation of different data sources and time trends (PDF link)…

“we have noticed that the figures provided in various reports for the UK’s share of the world’s production of scientific publications vary enormously. That a seemingly straightforward figure should show such volatility perplexed us, and so we asked Grant Lewison and colleagues in the CIBER group at University College London to analyse the published figures, and explain the differences between them.”