| Year | Value | | 2021 | 0.684174704 | | 2020 | 4.34740656 | | 2019 | 16.55784 | | 2018 | 16.916 | | 2017 | 19.484 | | 2016 | 5.953543762 | | 2015 | 4.8118552898892 | | 2014 | 4.170145075942 | | 2012 | 2.7792137733545 | | 2011 | 3.1219583241899 | | 2010 | 6.19 | | 2009 | 9.234 | | 2008 | 10.513 | | 2007 | 11.028 | | 2006 | 10.461 | | 2005 | 10.088 | | 2004 | 9.563 | | 2003 | 13.556 | | 2002 | 12.918 | | 2001 | 12.918 | | 2000 | 11.944 | | 1999 | 6.9000000954 | | 1998 | 3.2999999523 | | 1997 | 2.0999999046 | | 1996 | 2.0999999046 | | 1995 | 2.2999999523 | | 1994 | 2.2999999523 | | 1993 | 2.2999999523 |
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