| Year | Value | | 2022 | 19.880582316167 | | 2021 | 18.994394193458 | | 2020 | 22.706860536111 | | 2019 | 23.567863940691 | | 2018 | 22.007622605916 | | 2017 | 22.417827179951 | | 2016 | 22.511233347674 | | 2015 | 23.488712091646 | | 2014 | 20.631387441108 | | 2013 | 17.949973084374 | | 2012 | 19.260511388305 | | 2011 | 19.020031490542 | | 2010 | 15.873067852106 | | 2009 | 14.635671044125 | | 2008 | 16.529359205356 | | 2007 | 15.169915346915 | | 2006 | 15.122763350107 | | 2005 | 14.212945185454 | | 2004 | 12.976693563441 | | 2003 | 9.6811612455141 | | 2002 | 8.6101264603467 | | 2001 | 9.7268706566313 | | 2000 | 10.366695320772 | | 1999 | 13.663637673975 | | 1998 | 11.843186798435 | | 1997 | 7.537212931771 | | 1996 | 4.9446832954549 | | 1995 | 3.2880713277891 | | 1994 | -4.6595044552892 |
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