| Year | Value | | 2022 | 50.645728360006 | | 2021 | 50.628378413599 | | 2020 | 50.614847903924 | | 2019 | 50.550234897096 | | 2018 | 50.553626273789 | | 2017 | 50.601426632276 | | 2016 | 50.572917297522 | | 2015 | 50.546922861633 | | 2014 | 50.525243961742 | | 2013 | 50.507701638648 | | 2012 | 50.499774580209 | | 2011 | 50.496248273618 | | 2010 | 50.489404702283 | | 2009 | 50.479578532618 | | 2008 | 50.468274926183 | | 2007 | 50.457223657368 | | 2006 | 50.444545389859 | | 2005 | 50.429505500499 | | 2004 | 50.413838173402 | | 2003 | 50.404652728471 | | 2002 | 50.407533631642 | | 2001 | 50.41827861791 | | 2000 | 50.433073372327 | | 1999 | 50.452298321801 | | 1998 | 50.474563003548 | | 1997 | 50.499263796793 | | 1996 | 50.525047969369 | | 1995 | 50.553309691231 | | 1994 | 50.581499339481 | | 1993 | 50.607215502415 | | 1992 | 50.63540726659 | | 1991 | 50.656690184425 | | 1990 | 50.670751073486 | | 1989 | 50.679001651556 | | 1988 | 50.68284225176 | | 1987 | 50.686857799196 | | 1986 | 50.69102111108 | | 1985 | 50.698772329834 | | 1984 | 50.709191787873 | | 1983 | 50.721406924207 | | 1982 | 50.733571068293 | | 1981 | 50.747191941454 | | 1980 | 50.768200422037 | | 1979 | 50.7934511846 | | 1978 | 50.81826552744 | | 1977 | 50.841850212645 | | 1976 | 50.861331823705 | | 1975 | 50.878707057266 | | 1974 | 50.898032307508 | | 1973 | 50.917502358682 | | 1972 | 50.936002225517 | | 1971 | 50.961747463512 | | 1970 | 51.008758984389 | | 1969 | 51.054307774084 | | 1968 | 51.083993670074 | | 1967 | 51.11401875543 | | 1966 | 51.144714712561 | | 1965 | 51.179473679058 | | 1964 | 51.221056888124 | | 1963 | 51.271530112001 | | 1962 | 51.328502526097 | | 1961 | 51.384228530184 | | 1960 | 51.446031387402 |
|