| Year | Value | | 2021 | 8.986214020381 | | 2020 | 8.9901869251703 | | 2019 | 9.0001191871437 | | 2018 | 9.0274329075704 | | 2017 | 9.1369096389431 | | 2016 | 9.1480488531427 | | 2015 | 9.1467834341148 | | 2014 | 9.1380337636544 | | 2013 | 9.1837140019861 | | 2012 | 9.1185712087443 | | 2011 | 9.1506998907972 | | 2010 | 9.1625219644399 | | 2009 | 9.1458269217405 | | 2008 | 9.1039501245893 | | 2007 | 8.6891757696127 | | 2006 | 8.8381330685204 | | 2005 | 8.7388282025819 | | 2004 | 8.7388282025819 | | 2003 | 8.5898709036743 | | 2002 | 8.3416087388282 | | 2001 | 8.5898709036743 | | 2000 | 8.5898709036743 | | 1999 | 8.4905660377358 | | 1998 | 8.5402184707051 | | 1997 | 8.5898709036743 | | 1996 | 9.4836146971202 | | 1995 | 9.7318768619662 | | 1994 | 9.7318768619662 | | 1993 | 9.9304865938431 | | 1992 | 9.9304865938431 |
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