| Year | Value | | 2021 | 0.28684375405365 | | 2020 | 4.0710456972205 | | 2019 | 7.4816903901583 | | 2018 | 9.7779604752203 | | 2017 | 8.2726859763725 | | 2016 | 8.4912229117036 | | 2015 | 4.3232115642042 | | 2014 | 7.8793764814756 | | 2013 | 5.6621181873002 | | 2012 | 7.7711860324647 | | 2011 | 9.0315020894794 | | 2010 | 17.963825985187 | | 2009 | 4.7212175291736 | | 2008 | 5.7787946718794 | | 2007 | 8.1929570999246 | | 2006 | 6.7045997098215 | | 2005 | 8.2863246378151 | | 2004 | 3.2372019527668 | | 2003 | 3.2934936828506 | | 2002 | 5.6931500401931 | | 2001 | 6.511520843506 | | 2000 | 1.3908901311795 | | 1999 | 3.7131540912545 | | 1998 | 6.6851537178838 | | 1997 | 8.6167058702273 | | 1996 | 7.0546442087106 |
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