| Year | Value | | 2022 | 9.5252662862283 | | 2021 | 4.2227896203322 | | 2020 | 3.5828745455939 | | 2019 | 2.7826116365711 | | 2018 | 3.0673599605836 | | 2017 | 4.1807233187127 | | 2016 | 3.5231731762847 | | 2015 | 3.2547268811763 | | 2014 | 3.9924658414899 | | 2013 | 5.0096464534495 | | 2012 | 5.9817213231556 | | 2011 | 6.7167684358855 | | 2010 | 4.7631162752545 | | 2009 | 4.4462624422926 | | 2008 | 11.403427081393 | | 2007 | 7.0255143697477 | | 2006 | 6.6952646577335 | | 2005 | 7.1654175994664 | | 2004 | 4.6013399824979 | | 2003 | 5.6878585265811 | | 2002 | 4.1786723990479 | | 2001 | 4.6037462196468 | | 2000 | 4.0121208107034 | | 1999 | 4.5780301536216 | | 1998 | 6.2090415905957 | | 1997 | 7.2173291119174 | | 1996 | 8.5199519592534 | | 1995 | 11.386907492485 | | 1994 | 22.453069018124 | | 1993 | 9.5248453701969 | | 1992 | 10.141817562151 | | 1991 | 12.275172943889 | | 1990 | 9.8608510839836 | | 1989 | 8.8133620506529 | | 1988 | 9.4535133900969 | | 1987 | 7.9347540718007 | | 1986 | 9.6829547311652 | | 1985 | 9.3293611298432 | | 1984 | 8.8233959889378 |
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