| Year | Value | | 2022 | 15.156658649614 | | 2021 | 14.874336327741 | | 2020 | 14.664978065993 | | 2019 | 14.685468226538 | | 2018 | 14.577547064241 | | 2017 | 14.353232562121 | | 2016 | 13.940651649321 | | 2015 | 13.688326817645 | | 2014 | 13.17118796123 | | 2013 | 12.729151246223 | | 2012 | 12.466002397181 | | 2011 | 12.090430895996 | | 2010 | 11.782202924793 | | 2009 | 11.402074417824 | | 2008 | 11.014164604734 | | 2007 | 10.563422020394 | | 2006 | 10.148619726939 | | 2005 | 9.6586126079577 | | 2004 | 9.2212961917449 | | 2003 | 8.7990523504979 | | 2002 | 8.4439312984952 | | 2001 | 8.4631339052036 | | 2000 | 8.1071235541698 | | 1999 | 7.934650728184 | | 1998 | 7.6975415681806 | | 1997 | 7.5042630280024 | | 1996 | 7.3420844595021 | | 1995 | 7.2151310374344 | | 1994 | 7.1649226446909 | | 1993 | 7.0739353848844 | | 1992 | 7.0554062125458 | | 1991 | 7.0280849047591 |
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