| Year | Value | | 2021 | 42.763367744429 | | 2020 | 42.856379439107 | | 2019 | 43.188034329673 | | 2018 | 42.849631945733 | | 2017 | 43.060696938539 | | 2016 | 43.057712965989 | | 2015 | 43.30510294967 | | 2014 | 43.369228777105 | | 2013 | 43.944967572635 | | 2012 | 44.147139676092 | | 2011 | 44.296896204722 | | 2010 | 44.73504941346 | | 2009 | 44.942510938111 | | 2008 | 45.277631884418 | | 2007 | 45.016679867039 | | 2006 | 45.422843744397 | | 2005 | 45.950840981475 | | 2004 | 45.861112713285 | | 2003 | 46.071310576976 | | 2002 | 46.478253474048 | | 2001 | 46.785108973087 | | 2000 | 47.360743335895 | | 1999 | 47.598116395052 | | 1998 | 47.645049336715 | | 1997 | 47.657913309138 | | 1996 | 47.900953443688 | | 1995 | 47.84883459404 | | 1994 | 48.45553723082 | | 1993 | 48.617365458914 | | 1992 | 48.689556453119 | | 1991 | 49.452191441705 | | 1990 | 50.319257616083 | | 1989 | 50.565568144945 | | 1988 | 50.59814121859 | | 1987 | 50.918436193706 | | 1986 | 50.992960066657 | | 1985 | 51.119434879994 | | 1984 | 51.214913405417 | | 1983 | 51.317783395215 | | 1982 | 51.74635869254 | | 1981 | 51.823371588051 | | 1980 | 51.879837144958 | | 1979 | 52.022600210949 | | 1978 | 52.165924775192 | | 1977 | 52.156206510527 | | 1976 | 52.204642470673 | | 1975 | 52.519504961505 | | 1974 | 52.689650479862 | | 1973 | 52.844120207144 | | 1972 | 53.071643185554 | | 1971 | 53.268340202447 | | 1970 | 54.087987168434 | | 1969 | 54.686749317307 | | 1968 | 54.653226602763 | | 1967 | 54.977417805042 | | 1966 | 55.019653106286 | | 1965 | 55.147686642277 | | 1964 | 55.305633392607 | | 1963 | 55.562281303702 | | 1962 | 55.651066711032 | | 1961 | 55.681726718516 |
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