| Year | Value | | 2020 | 11.340431962926 | | 2019 | 11.996995764392 | | 2018 | 12.244241666196 | | 2017 | 11.577031156491 | | 2016 | 11.058329312953 | | 2015 | 11.690563267295 | | 2014 | 11.252185823349 | | 2013 | 10.671836497112 | | 2012 | 15.368181010655 | | 2011 | 14.865790361573 | | 2010 | 13.388387403293 | | 2009 | 12.612461522059 | | 2008 | 13.895967907455 | | 2007 | 13.877984546399 | | 2006 | 12.534618528847 | | 2005 | 21.321508315786 | | 2004 | 21.752105518845 | | 2003 | 18.477686134796 | | 2002 | 17.493111211166 | | 2001 | 17.19292789468 | | 1993 | 13.149247178534 | | 1992 | 10.768657182357 | | 1991 | 13.159595621721 | | 1990 | 11.436798693871 |
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