| Year | Value | | 2022 | 48.778777941498 | | 2021 | 48.818965020976 | | 2020 | 48.879588075719 | | 2019 | 48.916397545672 | | 2018 | 48.934178414137 | | 2017 | 48.94739432568 | | 2016 | 48.954913066798 | | 2015 | 48.959489328568 | | 2014 | 48.962088085789 | | 2013 | 48.961999420824 | | 2012 | 48.960018965425 | | 2011 | 48.954741592372 | | 2010 | 48.95159661616 | | 2009 | 48.954503394651 | | 2008 | 48.957968888381 | | 2007 | 48.959241405127 | | 2006 | 48.95805927 | | 2005 | 48.954972592525 | | 2004 | 48.949773474762 | | 2003 | 48.943588341548 | | 2002 | 48.937559935964 | | 2001 | 48.93192655095 | | 2000 | 48.940814812664 | | 1999 | 48.962860880714 | | 1998 | 48.983774822543 | | 1997 | 49.006063267227 | | 1996 | 49.031438075163 | | 1995 | 49.059186365808 | | 1994 | 49.086025856886 | | 1993 | 49.113471127763 | | 1992 | 49.142981663796 | | 1991 | 49.174736248299 | | 1990 | 49.205405532139 | | 1989 | 49.237135859126 | | 1988 | 49.273413792258 | | 1987 | 49.31064623463 | | 1986 | 49.349868641084 | | 1985 | 49.389313811092 | | 1984 | 49.429155020923 | | 1983 | 49.470118816082 | | 1982 | 49.512886823619 | | 1981 | 49.558071870968 | | 1980 | 49.603875248197 | | 1979 | 49.650486854362 | | 1978 | 49.69748376727 | | 1977 | 49.741824553959 | | 1976 | 49.801808999168 | | 1975 | 49.874415340779 | | 1974 | 49.941300406632 | | 1973 | 50.007491643355 | | 1972 | 50.074868187391 | | 1971 | 50.150007683389 | | 1970 | 50.195136914397 | | 1969 | 50.202562306328 | | 1968 | 50.209272407785 | | 1967 | 50.215959392656 | | 1966 | 50.222873531106 | | 1965 | 50.230508027389 | | 1964 | 50.239212976823 | | 1963 | 50.249291445741 | | 1962 | 50.261111498732 | | 1961 | 50.274736582401 | | 1960 | 50.289826680808 |
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