| Year | Value | | 2021 | 9.0005455899275 | | 2017 | 10.749673306969 | | 2016 | 10.088174833175 | | 2015 | 10.545750319078 | | 2014 | 10.551655106566 | | 2013 | 10.50429012814 | | 2012 | 10.805994525413 | | 2010 | 10.158689469661 | | 2009 | 9.7500019358893 | | 2008 | 9.5369860663991 | | 2007 | 9.8502218762192 | | 2006 | 10.576708061327 | | 2005 | 11.332937368474 | | 2004 | 11.211717494541 | | 2002 | 12.741631840218 | | 1991 | 12.42805492458 |
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