| Year | Value | | 2022 | 0.2251091217167 | | 2021 | 0.25147587490805 | | 2020 | 0.2692870134245 | | 2019 | 0.27863392059892 | | 2018 | 0.28717396749053 | | 2017 | 0.30682097413841 | | 2016 | 0.33518953102215 | | 2015 | 0.34185640314252 | | 2014 | 0.46082418557442 | | 2013 | 0.5018455932297 | | 2012 | 0.51299596010495 | | 2011 | 0.54477735623716 | | 2010 | 0.57476072166162 | | 2009 | 0.60116902064184 | | 2008 | 0.57698782020319 | | 2007 | 0.50875479416122 | | 2006 | 0.51315124388682 | | 2005 | 0.5406126988173 | | 2004 | 0.56832229211007 | | 2003 | 0.58754093593682 | | 2002 | 0.63401372038608 | | 2001 | 0.70351715626936 | | 2000 | 0.69569774211355 | | 1999 | 0.7506764986593 | | 1998 | 0.82386951599408 | | 1997 | 0.92406612738302 | | 1996 | 0.98992715896719 | | 1995 | 1.014359388261 | | 1994 | 1.1087325911852 | | 1993 | 1.139225148701 | | 1992 | 1.204118549852 | | 1991 | 1.2539353125599 | | 1990 | 1.2035032840438 | | 1989 | 1.1054761194708 | | 1988 | 1.1994341526595 | | 1987 | 1.2823002469903 | | 1986 | 1.4232052652489 | | 1985 | 1.4160442040808 | | 1984 | 1.4124394252766 | | 1983 | 1.4926312327501 | | 1982 | 1.5912369478854 | | 1981 | 1.580606618441 | | 1980 | 1.665267012221 | | 1979 | 1.5822005670923 | | 1978 | 1.48308354739 | | 1977 | 1.5251774400585 | | 1976 | 1.6151624994801 | | 1975 | 1.6259589671087 | | 1974 | 1.4069323563694 | | 1973 | 1.312694901055 | | 1972 | 1.3288110113196 | | 1971 | 1.2439451322746 | | 1970 | 1.1586092960281 | | 1969 | 1.099280370991 | | 1968 | 1.1328512994364 | | 1967 | 1.1871268479786 | | 1966 | 1.2343604576354 | | 1965 | 1.3269080550052 | | 1964 | 1.3032078648906 | | 1963 | 1.2428171338392 | | 1962 | 1.2902199760963 | | 1961 | 1.3201420849705 | | 1960 | 1.3303867427439 |
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