| Year | Value | | 2022 | 50.510230158102 | | 2021 | 50.495621911325 | | 2020 | 50.478502271361 | | 2019 | 50.471076860518 | | 2018 | 50.471425342976 | | 2017 | 50.470075409306 | | 2016 | 50.467828747694 | | 2015 | 50.464727221685 | | 2014 | 50.460603268223 | | 2013 | 50.455154888307 | | 2012 | 50.448311926002 | | 2011 | 50.440264987525 | | 2010 | 50.430756919371 | | 2009 | 50.419719299766 | | 2008 | 50.407444469744 | | 2007 | 50.394484589832 | | 2006 | 50.380848894673 | | 2005 | 50.366966287652 | | 2004 | 50.353108157862 | | 2003 | 50.339127213992 | | 2002 | 50.325789008431 | | 2001 | 50.312802008195 | | 2000 | 50.299099497661 | | 1999 | 50.284398208436 | | 1998 | 50.268874409515 | | 1997 | 50.252393749471 | | 1996 | 50.235033966803 | | 1995 | 50.216914067136 | | 1994 | 50.198223443254 | | 1993 | 50.170740697495 | | 1992 | 50.133303677807 | | 1991 | 50.093686120359 | | 1990 | 50.057095493782 | | 1989 | 50.024797676078 | | 1988 | 49.992424516381 | | 1987 | 49.958724437559 | | 1986 | 49.922148306647 | | 1985 | 49.884237445294 | | 1984 | 49.844208509139 | | 1983 | 49.795541775026 | | 1982 | 49.685508517222 | | 1981 | 49.560365763627 | | 1980 | 49.483747812427 | | 1979 | 49.419176174154 | | 1978 | 49.362468546814 | | 1977 | 49.313574074791 | | 1976 | 49.27907968908 | | 1975 | 49.249064858312 | | 1974 | 49.215564117928 | | 1973 | 49.189386237827 | | 1972 | 49.165608427385 | | 1971 | 49.137041293622 | | 1970 | 49.104545434541 | | 1969 | 49.068194037482 | | 1968 | 49.032102798346 | | 1967 | 48.999375823152 | | 1966 | 48.969123051066 | | 1965 | 48.941449829601 | | 1964 | 48.917912083286 | | 1963 | 48.898031063633 | | 1962 | 48.880846840156 | | 1961 | 48.866484834139 | | 1960 | 48.853978379602 |
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