| Year | Value | | 2022 | 3.1565074996313 | | 2021 | 1.8347155481044 | | 2020 | 3.2209343665251 | | 2019 | 2.7958236745225 | | 2018 | 3.5396280594264 | | 2017 | 3.5202568881162 | | 2016 | 2.6682481696908 | | 2015 | 0.63120090517575 | | 2014 | 4.0845544663762 | | 2013 | 6.5926747589919 | | 2012 | 9.0947033955719 | | 2011 | 18.677732277071 | | 2010 | 9.2074664877841 | | 2009 | 6.7169826998863 | | 2008 | 23.115448347448 | | 2007 | 8.3444488977384 | | 2006 | 7.4180171510846 | | 2005 | 8.2845724312868 | | 2004 | 7.754947487096 | | 2003 | 3.2346481729393 | | 2002 | 3.8308283816847 | | 2001 | 0.43154451172818 | | 2000 | -1.7103372785111 | | 1999 | 4.1171023577174 | | 1998 | 7.2661980440096 | | 1997 | 3.2095260626137 | | 1996 | 5.6749999999999 |
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