The new Excellence Indicator in the World Report of the SCImago   Institutions Rankings 2011
  The new excellence indicator in the World Report of the SCImago Institutions Rankings (SIR) makes it possible to test differences in the ranking in terms of statistical significance. For example, at the 17th position of these rankings, UCLA has an output of 37,994 papers with an excellence indicator of 28.9. Stanford University follows at the 19th position with 37,885 papers and 29.1 excellence, and z = - 0.607. The difference between these two institution thus is not statistically significant. We provide a calculator at http://www.leydesdorff.net/scimago11/scimago11.xls in which one can fill out this test for any two institutions and also for each institution on whether its score is significantly above or below expectation (assuming that 10% of the papers are for stochastic reasons in the top-10% set). 
Lutz Bornmann, Felix de Moya-Aneg\'on, and Loet Leydesdorff
cs.DL