| Year | Value | | 2022 | 18.005635112285 | | 2021 | 8.1377703837872 | | 2020 | 9.8193279154017 | | 2019 | 7.720245252132 | | 2018 | 7.8685962887391 | | 2017 | 5.6902961992903 | | 2016 | 5.4305196611917 | | 2015 | 5.2458783502246 | | 2014 | 6.9984994396641 | | 2013 | 8.1058327087548 | | 2012 | 10.637935343163 | | 2011 | 14.32716676168 | | 2010 | 13.34005235378 | | 2009 | 16.957475802595 | | 2008 | 31.990103949257 | | 2007 | 18.548513632578 | | 2006 | 23.077037345138 | | 2005 | 17.152204935435 | | 2004 | 13.28588608718 | | 2003 | 9.7924197493451 | | 2002 | 10.128724672229 | | 2001 | 9.2220370756089 | | 2000 | 12.208945630898 | | 1999 | 12.725177013008 | | 1998 | 50.493135748625 | | 1997 | 35.81717824448 |
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