| Year | Value | | 2022 | 49.120633304758 | | 2021 | 49.067884172889 | | 2020 | 49.017021486339 | | 2019 | 48.977588132612 | | 2018 | 48.943345200665 | | 2017 | 48.91162803737 | | 2016 | 48.897136716125 | | 2015 | 48.913319434838 | | 2014 | 48.964768628089 | | 2013 | 49.051269407526 | | 2012 | 49.160806988602 | | 2011 | 49.279830747532 | | 2010 | 49.399890713895 | | 2009 | 49.516069141274 | | 2008 | 49.626119859148 | | 2007 | 49.732348071396 | | 2006 | 49.833747522519 | | 2005 | 49.925429577064 | | 2004 | 50.006209821397 | | 2003 | 50.074289138551 | | 2002 | 50.134680285251 | | 2001 | 50.191643897474 | | 2000 | 50.242392580925 | | 1999 | 50.289096073065 | | 1998 | 50.334674566386 | | 1997 | 50.377519693916 | | 1996 | 50.417651297018 | | 1995 | 50.456610016008 | | 1994 | 50.486141781676 | | 1993 | 50.506293469997 | | 1992 | 50.52764192064 | | 1991 | 50.54906212407 | | 1990 | 50.569363232787 | | 1989 | 50.589382849508 | | 1988 | 50.60926591464 | | 1987 | 50.629049652161 | | 1986 | 50.648385850921 | | 1985 | 50.667381217585 | | 1984 | 50.686151110428 | | 1983 | 50.705710037505 | | 1982 | 50.725254405796 | | 1981 | 50.742745518296 | | 1980 | 50.758932981612 | | 1979 | 50.774868937863 | | 1978 | 50.789808112226 | | 1977 | 50.805619550718 | | 1976 | 50.821619072879 | | 1975 | 50.837127265053 | | 1974 | 50.852953051368 | | 1973 | 50.868739847125 | | 1972 | 50.885681733085 | | 1971 | 50.904307577748 | | 1970 | 50.922651341612 | | 1969 | 50.940427074995 | | 1968 | 50.956310112602 | | 1967 | 50.969817658689 | | 1966 | 50.983719239655 | | 1965 | 50.997835754792 | | 1964 | 51.009762332586 | | 1963 | 51.021983056448 | | 1962 | 51.036035864682 | | 1961 | 51.049334814732 | | 1960 | 51.060700510383 |
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