| Year | Value | | 2022 | 49.719547702179 | | 2021 | 49.724709784411 | | 2020 | 49.729678703831 | | 2019 | 49.732942827929 | | 2018 | 49.734594766825 | | 2017 | 49.735553691097 | | 2016 | 49.738356787501 | | 2015 | 49.745366429661 | | 2014 | 49.755711659183 | | 2013 | 49.767937178205 | | 2012 | 49.774099770728 | | 2011 | 49.782662680727 | | 2010 | 49.805837164148 | | 2009 | 49.763399904584 | | 2008 | 49.647487145724 | | 2007 | 49.530345747157 | | 2006 | 49.409081068946 | | 2005 | 49.281593743849 | | 2004 | 49.1498880972 | | 2003 | 49.013412096507 | | 2002 | 48.869156923363 | | 2001 | 48.717051751445 | | 2000 | 48.558104619521 | | 1999 | 48.454607930574 | | 1998 | 48.408728482057 | | 1997 | 48.361561717759 | | 1996 | 48.311310738301 | | 1995 | 48.254663548721 | | 1994 | 48.19210516488 | | 1993 | 48.122649962093 | | 1992 | 48.047503973064 | | 1991 | 47.972880519209 | | 1990 | 47.901185803277 | | 1989 | 47.819628647215 | | 1988 | 47.726005214688 | | 1987 | 47.627309172455 | | 1986 | 47.521865042365 | | 1985 | 47.410805180743 | | 1984 | 47.295311396148 | | 1983 | 47.173619440978 | | 1982 | 47.042311357904 | | 1981 | 46.903312460747 | | 1980 | 46.904808437935 | | 1979 | 47.095017436583 | | 1978 | 47.329194539359 | | 1977 | 47.567625222616 | | 1976 | 47.810693288601 | | 1975 | 48.05749486653 | | 1974 | 48.301191320662 | | 1973 | 48.541567092593 | | 1972 | 48.783429576373 | | 1971 | 48.97088635628 | | 1970 | 48.991861088484 | | 1969 | 48.850009334923 | | 1968 | 48.653714811735 | | 1967 | 48.450016881004 | | 1966 | 48.240154140137 | | 1965 | 48.027900194957 | | 1964 | 47.817754122913 | | 1963 | 47.605478685745 | | 1962 | 47.390782178397 | | 1961 | 47.212134756132 | | 1960 | 47.114830187421 |
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