| Year | Value | | 2022 | 49.378739122897 | | 2021 | 49.363454118589 | | 2020 | 49.35230179681 | | 2019 | 49.333960608104 | | 2018 | 49.305440259051 | | 2017 | 49.274972521067 | | 2016 | 49.250940309877 | | 2015 | 49.228495413139 | | 2014 | 49.21247615441 | | 2013 | 49.202129818634 | | 2012 | 49.185883218222 | | 2011 | 49.16358057522 | | 2010 | 49.129927177596 | | 2009 | 49.081379816564 | | 2008 | 49.022278460833 | | 2007 | 48.954207395409 | | 2006 | 48.883291578179 | | 2005 | 48.819398913888 | | 2004 | 48.761837140314 | | 2003 | 48.702940505117 | | 2002 | 48.643607983823 | | 2001 | 48.582974351989 | | 2000 | 48.520456170725 | | 1999 | 48.456097869538 | | 1998 | 48.391404476297 | | 1997 | 48.327481205468 | | 1996 | 48.265261169951 | | 1995 | 48.206375345451 | | 1994 | 48.148441282729 | | 1993 | 48.081465564995 | | 1992 | 48.009882487093 | | 1991 | 48.007075266699 | | 1990 | 48.071897032667 | | 1989 | 48.137202104065 | | 1988 | 48.203242440964 | | 1987 | 48.267602783111 | | 1986 | 48.326624340796 | | 1985 | 48.376487656142 | | 1984 | 48.414621942011 | | 1983 | 48.439781770255 | | 1982 | 48.459006714506 | | 1981 | 48.394551191711 | | 1980 | 48.216344299568 | | 1979 | 47.995635142697 | | 1978 | 47.747806082925 | | 1977 | 47.477966908229 | | 1976 | 47.186152834462 | | 1975 | 46.873188356023 | | 1974 | 46.539246264653 | | 1973 | 46.183012144616 | | 1972 | 45.839537440891 | | 1971 | 45.638503721826 | | 1970 | 45.728449760572 | | 1969 | 46.034765150314 | | 1968 | 46.388686272322 | | 1967 | 46.747062065963 | | 1966 | 47.108401249011 | | 1965 | 47.470554752835 | | 1964 | 47.671064285384 | | 1963 | 47.711190967523 | | 1962 | 47.75626924769 | | 1961 | 47.809795138472 | | 1960 | 47.873416981077 |
|