| Year | Value | | 2021 | 24.35982900521 | | 2020 | 24.270228273336 | | 2019 | 24.180627541462 | | 2018 | 24.091026809588 | | 2017 | 24.001426077714 | | 2016 | 23.911825345841 | | 2015 | 23.822224613967 | | 2014 | 23.732623882093 | | 2013 | 23.643023150219 | | 2012 | 23.553422418345 | | 2011 | 23.463821686471 | | 2010 | 23.374220954598 | | 2009 | 23.31014835917 | | 2008 | 23.246075763742 | | 2007 | 23.182003168314 | | 2006 | 23.117930572886 | | 2005 | 23.053857977459 | | 2004 | 22.989785382031 | | 2003 | 22.925712786603 | | 2002 | 22.861640191175 | | 2001 | 22.797567595747 | | 2000 | 22.73349500032 | | 1999 | 22.610630333077 | | 1998 | 22.487765665834 | | 1997 | 22.364900998591 | | 1996 | 22.242036331348 | | 1995 | 22.119171664105 | | 1994 | 21.996306996862 | | 1993 | 21.873442329619 | | 1992 | 21.750577662376 | | 1991 | 21.627712995133 | | 1990 | 21.50484832789 |
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