| Year | Value | | 2022 | 1.2772739162567 | | 2021 | 1.3224589477115 | | 2020 | 1.3566919563676 | | 2019 | 1.2700496139222 | | 2018 | 1.2548419162331 | | 2017 | 1.531645542806 | | 2016 | 1.4859866220862 | | 2015 | 1.6620339421847 | | 2014 | 1.6251039964436 | | 2013 | 1.6275054463968 | | 2012 | 1.6499262864395 | | 2011 | 1.6418798144518 | | 2010 | 2.3325376726732 | | 2009 | 2.5625714687031 | | 2008 | 2.3893508666172 | | 2007 | 2.5077252879663 | | 2006 | 2.4537252747511 | | 2005 | 2.5497471979063 | | 2004 | 2.8368246657071 | | 2003 | 2.8594834487623 | | 2002 | 2.9566605495948 | | 2001 | 3.0759548379761 | | 2000 | 3.0855079137344 | | 1999 | 3.321972516131 | | 1998 | 3.2788065347114 | | 1997 | 2.9034854380711 | | 1996 | 2.9872076198473 | | 1995 | 3.4789922908431 | | 1994 | 3.9832571765041 | | 1993 | 3.5867532831766 | | 1992 | 3.7418969483712 | | 1991 | 4.0987301993164 | | 1990 | 3.6548132390791 | | 1989 | 3.3525355407903 | | 1988 | 3.2408028810922 | | 1987 | 4.3948924180186 | | 1986 | 4.93492933954 | | 1985 | 4.9858112845312 | | 1984 | 5.1012150249625 | | 1983 | 4.6855197557232 | | 1982 | 4.7287278406179 | | 1981 | 4.0691277998849 | | 1980 | 3.8856794186042 | | 1979 | 3.5045542214051 | | 1978 | 3.2888119732745 | | 1977 | 3.2861667927152 | | 1976 | 3.4403969592775 | | 1975 | 2.8378924861087 | | 1974 | 2.5213484162747 | | 1973 | 2.5701190317835 |
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