| Year | Value | | 2022 | 50.085322707581 | | 2021 | 50.094843582541 | | 2020 | 50.097999457141 | | 2019 | 50.102502043489 | | 2018 | 50.107238802501 | | 2017 | 50.113562045167 | | 2016 | 50.121225898872 | | 2015 | 50.129656557378 | | 2014 | 50.139551707113 | | 2013 | 50.151261577743 | | 2012 | 50.164051321528 | | 2011 | 50.178356490791 | | 2010 | 50.193071227832 | | 2009 | 50.207650910177 | | 2008 | 50.221759069434 | | 2007 | 50.234494651124 | | 2006 | 50.246722613242 | | 2005 | 50.257356198493 | | 2004 | 50.266171041562 | | 2003 | 50.27714856363 | | 2002 | 50.290421227232 | | 2001 | 50.304659872255 | | 2000 | 50.317795988583 | | 1999 | 50.328924747482 | | 1998 | 50.338123223631 | | 1997 | 50.348532762832 | | 1996 | 50.360859564387 | | 1995 | 50.373647575848 | | 1994 | 50.390976583857 | | 1993 | 50.407092352234 | | 1992 | 50.420145234284 | | 1991 | 50.439896523977 | | 1990 | 50.460951706717 | | 1989 | 50.483962382635 | | 1988 | 50.498986009661 | | 1987 | 50.507637865148 | | 1986 | 50.521453731604 | | 1985 | 50.539522654248 | | 1984 | 50.558146750454 | | 1983 | 50.575612720555 | | 1982 | 50.596982736493 | | 1981 | 50.624195816943 | | 1980 | 50.670540894207 | | 1979 | 50.717821938472 | | 1978 | 50.736970605724 | | 1977 | 50.753324735739 | | 1976 | 50.778885227145 | | 1975 | 50.808003409083 | | 1974 | 50.838471906838 | | 1973 | 50.867272317189 | | 1972 | 50.892299284838 | | 1971 | 50.918045414005 | | 1970 | 50.933926513358 | | 1969 | 50.944633183735 | | 1968 | 50.962433937651 | | 1967 | 50.98016701658 | | 1966 | 50.99972849661 | | 1965 | 51.0224020622 | | 1964 | 51.044998991764 | | 1963 | 51.068806698291 | | 1962 | 51.094922894972 | | 1961 | 51.118764670591 | | 1960 | 51.138030494106 |
|