According to a ranking of universities produced by SCImago Research Group, UCL is ranked 12th in the world (and 1st in Europe) in terms of total research output. According to data released in July 2008 by ISI Web of Knowledge, UCL is the 13th most-cited university in the world (and most-cited in Europe). The analysis covered citations from 1 January 1998 to 30 April 2008, during which 46,166 UCL research papers attracted 803,566 citations. The report covered citations in 21 subject areas and the results revealed some of UCL's key strengths, including: Clinical Medicine (1st outside North America); Immunology (2nd in Europe); Neuroscience & Behaviour (1st outside North America and 2nd in the world); Pharmacology & Toxicology (1st outside North America and 4th in the world); Psychiatry & Psychology (2nd outside North America); and Social Sciences, General (1st outside North America).