| Year | Value | | 2022 | 50.135195307206 | | 2021 | 50.149035809693 | | 2020 | 50.181112576623 | | 2019 | 50.232289744302 | | 2018 | 50.302286408211 | | 2017 | 50.371755099731 | | 2016 | 50.440290470845 | | 2015 | 50.511665939817 | | 2014 | 50.584778714666 | | 2013 | 50.655698760637 | | 2012 | 50.725364658052 | | 2011 | 50.795999361483 | | 2010 | 50.86806994053 | | 2009 | 50.939389804334 | | 2008 | 51.009053997241 | | 2007 | 51.025657723365 | | 2006 | 50.993847690421 | | 2005 | 50.966542198571 | | 2004 | 50.940701100965 | | 2003 | 50.914708740239 | | 2002 | 50.890996610154 | | 2001 | 50.868991584653 | | 2000 | 50.846897751255 | | 1999 | 50.825700552086 | | 1998 | 50.804904987671 | | 1997 | 50.780539218367 | | 1996 | 50.761671131823 | | 1995 | 50.746106638595 | | 1994 | 50.724643179148 | | 1993 | 50.703372284268 | | 1992 | 50.682523806679 | | 1991 | 50.661288020876 | | 1990 | 50.645413425932 | | 1989 | 50.636725059014 | | 1988 | 50.630584664495 | | 1987 | 50.627601758398 | | 1986 | 50.621281935965 | | 1985 | 50.615221984409 | | 1984 | 50.617188390581 | | 1983 | 50.621618153586 | | 1982 | 50.625805984634 | | 1981 | 50.629399209845 | | 1980 | 50.633588899473 | | 1979 | 50.640445632487 | | 1978 | 50.649026826442 | | 1977 | 50.657529172069 | | 1976 | 50.680438521872 | | 1975 | 50.720905030184 | | 1974 | 50.765853899727 | | 1973 | 50.815980073361 | | 1972 | 50.869290660281 | | 1971 | 50.923048327138 | | 1970 | 50.97851920081 | | 1969 | 51.03839428032 | | 1968 | 51.100144472399 | | 1967 | 51.161873877954 | | 1966 | 51.223987163062 | | 1965 | 51.284194366858 | | 1964 | 51.345521007702 | | 1963 | 51.410220102631 | | 1962 | 51.477571633992 | | 1961 | 51.549450708506 | | 1960 | 51.622905577081 |
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