| Year | Value | | 2021 | 2.9476787030214 | | 2020 | 2.9476787030214 | | 2019 | 2.9476787030214 | | 2018 | 2.9476787030214 | | 2017 | 2.9476787030214 | | 2016 | 2.9476787030214 | | 2015 | 2.9476787030214 | | 2014 | 2.9476787030214 | | 2013 | 2.9476787030214 | | 2012 | 2.9476787030214 | | 2011 | 2.9476787030214 | | 2010 | 2.9476787030214 | | 2009 | 2.9476787030214 | | 2008 | 3.0610509608299 | | 2007 | 3.0145683351284 | | 2006 | 3.0100334448161 | | 2005 | 3.0100334448161 | | 2004 | 3.0043648319256 | | 2003 | 2.9476787030214 | | 2002 | 2.9454112578652 | | 2001 | 2.9454112578652 | | 2000 | 2.9420100901309 | | 1999 | 2.9397426449748 | | 1998 | 2.9397426449748 | | 1997 | 2.9397426449748 | | 1996 | 2.9397426449748 | | 1995 | 2.9397426449748 | | 1994 | 2.9397426449748 | | 1993 | 2.9465449804433 | | 1992 | 2.9488124255995 | | 1991 | 3.2243070120742 | | 1990 | 3.2107023411371 | | 1989 | 3.2254407346522 | | 1988 | 3.5111388243297 | | 1987 | 3.5111388243297 | | 1986 | 3.4975341533927 | | 1985 | 3.3070687602744 | | 1984 | 3.0712544640326 | | 1983 | 3.0723881866107 | | 1982 | 3.1868941669973 | | 1981 | 3.1789581089507 | | 1980 | 3.3524176633978 | | 1979 | 3.3433478827731 | | 1978 | 3.3501502182416 | | 1977 | 3.3603537214444 | | 1976 | 3.3014001473839 | | 1975 | 3.2957315344935 | | 1974 | 3.2945978119154 | | 1973 | 3.2877954764469 | | 1972 | 3.2923303667592 | | 1971 | 3.3297432118361 | | 1970 | 3.3229408763676 | | 1969 | 3.315004818321 | | 1968 | 3.3093362054305 | | 1967 | 3.3127373731648 | | 1966 | 3.302533869962 | | 1965 | 3.3002664248059 | | 1964 | 3.2957315344935 | | 1963 | 3.2911966441812 | | 1962 | 3.2877954764469 | | 1961 | 3.2877954764469 |
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