| Year | Value | | 2022 | 49.911682684295 | | 2021 | 49.932387471508 | | 2020 | 49.976408007575 | | 2019 | 50.005171894874 | | 2018 | 50.010666637204 | | 2017 | 50.013343759193 | | 2016 | 50.014194397243 | | 2015 | 50.014052937589 | | 2014 | 50.013898990061 | | 2013 | 50.014631441897 | | 2012 | 50.016891757707 | | 2011 | 50.020948004847 | | 2010 | 50.027082137364 | | 2009 | 50.03472889687 | | 2008 | 50.042730128593 | | 2007 | 50.050186519841 | | 2006 | 50.056531269298 | | 2005 | 50.061692030479 | | 2004 | 50.065812839736 | | 2003 | 50.069362246248 | | 2002 | 50.07274718416 | | 2001 | 50.076279506296 | | 2000 | 50.080247846851 | | 1999 | 50.084651635999 | | 1998 | 50.089235852083 | | 1997 | 50.093861795597 | | 1996 | 50.098770969989 | | 1995 | 50.10415006189 | | 1994 | 50.109943449094 | | 1993 | 50.116012740338 | | 1992 | 50.122326630336 | | 1991 | 50.12877728534 | | 1990 | 50.135327469701 | | 1989 | 50.141824070769 | | 1988 | 50.147957007712 | | 1987 | 50.153206125449 | | 1986 | 50.156963638724 | | 1985 | 50.159033989673 | | 1984 | 50.15989730221 | | 1983 | 50.159955697405 | | 1982 | 50.159373922075 | | 1981 | 50.158106420011 | | 1980 | 50.155982568498 | | 1979 | 50.153020073235 | | 1978 | 50.149117340995 | | 1977 | 50.144131914772 | | 1976 | 50.137897299266 | | 1975 | 50.130428920882 | | 1974 | 50.121941108558 | | 1973 | 50.112321464523 | | 1972 | 50.101321929769 | | 1971 | 50.089199337925 | | 1970 | 50.076107199765 | | 1969 | 50.06197227064 | | 1968 | 50.046767209157 | | 1967 | 50.030838855756 | | 1966 | 50.014347421585 | | 1965 | 49.997311400356 | | 1964 | 49.979713629373 | | 1963 | 49.961702977991 | | 1962 | 49.94324624138 | | 1961 | 49.924392408556 | | 1960 | 49.905481795989 |
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