| Year | Value | | 2021 | 6.0378989840767 | | 2020 | 6.0479861661503 | | 2019 | 6.0825707904028 | | 2018 | 6.0479861661503 | | 2017 | 6.0371784710714 | | 2016 | 6.1675913250234 | | 2015 | 5.9716117875928 | | 2014 | 5.7657112388858 | | 2013 | 5.4972849385539 | | 2012 | 5.2772220634467 | | 2011 | 5.3100885967419 | | 2010 | 5.336524721349 | | 2009 | 5.3686767647899 | | 2008 | 5.2943698199486 | | 2007 | 5.3300943126608 | | 2006 | 5.2657902257788 | | 2005 | 5.4086881966276 | | 2004 | 5.5587310660189 | | 2003 | 5.5873106601886 | | 2002 | 5.5801657616462 | | 2001 | 5.5944555587311 | | 2000 | 5.6016004572735 | | 1999 | 5.6016004572735 | | 1998 | 5.6016004572735 | | 1997 | 5.7945127179194 | | 1996 | 5.7945127179194 | | 1995 | 6.03029436982 | | 1994 | 6.0731637610746 | | 1993 | 6.208916833381 | | 1992 | 6.144612746499 |
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