| Year | Value | | 2022 | 50.107578116892 | | 2021 | 50.120467724341 | | 2020 | 50.136992231144 | | 2019 | 50.151060680568 | | 2018 | 50.160715032697 | | 2017 | 50.169383962393 | | 2016 | 50.17869054908 | | 2015 | 50.18768132226 | | 2014 | 50.194478899568 | | 2013 | 50.200416926338 | | 2012 | 50.207072002011 | | 2011 | 50.214838506302 | | 2010 | 50.222020266453 | | 2009 | 50.228624491644 | | 2008 | 50.235707079033 | | 2007 | 50.242854046657 | | 2006 | 50.250241615344 | | 2005 | 50.258287222354 | | 2004 | 50.266627277465 | | 2003 | 50.274994542551 | | 2002 | 50.282926629382 | | 2001 | 50.289433163115 | | 2000 | 50.295138093046 | | 1999 | 50.299918739416 | | 1998 | 50.305954782707 | | 1997 | 50.315910789073 | | 1996 | 50.328882979748 | | 1995 | 50.344991669405 | | 1994 | 50.3632011836 | | 1993 | 50.38207373889 | | 1992 | 50.401774983736 | | 1991 | 50.421534814917 | | 1990 | 50.44149247677 | | 1989 | 50.46237860995 | | 1988 | 50.484471904735 | | 1987 | 50.507824835329 | | 1986 | 50.532562345585 | | 1985 | 50.559694424518 | | 1984 | 50.58932253269 | | 1983 | 50.620917920084 | | 1982 | 50.654340715758 | | 1981 | 50.690047905293 | | 1980 | 50.730064179854 | | 1979 | 50.810186267889 | | 1978 | 50.929968041866 | | 1977 | 51.05154790829 | | 1976 | 51.201939547315 | | 1975 | 51.24982135471 | | 1974 | 51.138209143714 | | 1973 | 51.003065196082 | | 1972 | 50.864099165229 | | 1971 | 50.704842692746 | | 1970 | 50.612881070561 | | 1969 | 50.618331495401 | | 1968 | 50.683676623901 | | 1967 | 50.759354082132 | | 1966 | 50.808619769784 | | 1965 | 50.851540880158 | | 1964 | 50.874563307968 | | 1963 | 50.896307504553 | | 1962 | 50.91999293096 | | 1961 | 50.948299348908 | | 1960 | 50.958951662209 |
|