| Year | Value | | 2022 | 48.371508459598 | | 2021 | 48.348035239045 | | 2020 | 48.37890451608 | | 2019 | 48.406002168282 | | 2018 | 48.41956480061 | | 2017 | 48.429378096278 | | 2016 | 48.429271505651 | | 2015 | 48.420907000319 | | 2014 | 48.416565328901 | | 2013 | 48.417819389545 | | 2012 | 48.420384684641 | | 2011 | 48.421963389735 | | 2010 | 48.425983875948 | | 2009 | 48.434974967163 | | 2008 | 48.441457092771 | | 2007 | 48.439599830893 | | 2006 | 48.429636984819 | | 2005 | 48.413688544767 | | 2004 | 48.395103527662 | | 2003 | 48.378824020125 | | 2002 | 48.372824350319 | | 2001 | 48.396767716064 | | 2000 | 48.441428227058 | | 1999 | 48.485673605893 | | 1998 | 48.534883559324 | | 1997 | 48.586684289286 | | 1996 | 48.636009961518 | | 1995 | 48.683179179603 | | 1994 | 48.724862562153 | | 1993 | 48.758567597362 | | 1992 | 48.78659730293 | | 1991 | 48.807677729592 | | 1990 | 48.821215442091 | | 1989 | 48.827481433243 | | 1988 | 48.828797874986 | | 1987 | 48.829157059562 | | 1986 | 48.830113636313 | | 1985 | 48.831306292378 | | 1984 | 48.829975218826 | | 1983 | 48.824054638681 | | 1982 | 48.813784743361 | | 1981 | 48.799346328517 | | 1980 | 48.779140043961 | | 1979 | 48.753215326006 | | 1978 | 48.722479088791 | | 1977 | 48.68582525705 | | 1976 | 48.676492630294 | | 1975 | 48.692851910722 | | 1974 | 48.701733359866 | | 1973 | 48.710617845855 | | 1972 | 48.722812572106 | | 1971 | 48.734485419983 | | 1970 | 48.744156014034 | | 1969 | 48.753302666977 | | 1968 | 48.763288165008 | | 1967 | 48.775359541414 | | 1966 | 48.783572006385 | | 1965 | 48.774964073996 | | 1964 | 48.752223297443 | | 1963 | 48.725788882666 | | 1962 | 48.695331732899 | | 1961 | 48.661178695425 | | 1960 | 48.624423610609 |
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