| Year | Value | | 2021 | 20.940540300824 | | 2020 | 22.992021036968 | | 2019 | 17.276048437938 | | 2018 | 16.168578985324 | | 2017 | 16.325374115885 | | 2016 | 14.241739579355 | | 2015 | 13.540765776856 | | 2014 | 11.200461282729 | | 2013 | 9.0672556404885 | | 2012 | 8.5514085934036 | | 2011 | 8.6410819443058 | | 2010 | 9.0981056447311 | | 2009 | 8.6978663350392 | | 2008 | 6.49528743789 | | 2007 | 7.158430116584 | | 2006 | 9.8910728604675 | | 2005 | 16.660868447798 | | 2002 | 41.352716864411 | | 2001 | 48.98361533517 | | 2000 | 62.148888866958 | | 1999 | 100.74413772421 | | 1998 | 143.94899953339 |
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