| Year | Value | | 2022 | 49.891548851589 | | 2021 | 49.898825991988 | | 2020 | 49.90548908971 | | 2019 | 49.912512110362 | | 2018 | 49.919828587733 | | 2017 | 49.928616690318 | | 2016 | 49.939597644115 | | 2015 | 49.951556938267 | | 2014 | 49.965787610381 | | 2013 | 49.981686635724 | | 2012 | 49.999580177731 | | 2011 | 50.020015470969 | | 2010 | 50.04227322767 | | 2009 | 50.066678999246 | | 2008 | 50.093517171631 | | 2007 | 50.122938198531 | | 2006 | 50.156994058633 | | 2005 | 50.193143672359 | | 2004 | 50.228027287009 | | 2003 | 50.261516412077 | | 2002 | 50.294127775012 | | 2001 | 50.324082538208 | | 2000 | 50.352361778307 | | 1999 | 50.340335341089 | | 1998 | 50.309743313165 | | 1997 | 50.315185283726 | | 1996 | 50.335099151901 | | 1995 | 50.348450064972 | | 1994 | 50.357929738748 | | 1993 | 50.373944668713 | | 1992 | 50.391764301652 | | 1991 | 50.410639698924 | | 1990 | 50.432331157344 | | 1989 | 50.457147267371 | | 1988 | 50.48119983778 | | 1987 | 50.504867820962 | | 1986 | 50.52755497972 | | 1985 | 50.548498314005 | | 1984 | 50.569244642091 | | 1983 | 50.589147723517 | | 1982 | 50.607589143613 | | 1981 | 50.625467689697 | | 1980 | 50.643345151281 | | 1979 | 50.661266314993 | | 1978 | 50.67854239499 | | 1977 | 50.695843099179 | | 1976 | 50.713667771437 | | 1975 | 50.73195729202 | | 1974 | 50.751072997153 | | 1973 | 50.770595986246 | | 1972 | 50.789602590138 | | 1971 | 50.807939014091 | | 1970 | 50.826202233749 | | 1969 | 50.841883796879 | | 1968 | 50.85601918896 | | 1967 | 50.870708091449 | | 1966 | 50.883670540476 | | 1965 | 50.894716128377 | | 1964 | 50.905088636406 | | 1963 | 50.915545482641 | | 1962 | 50.926302837618 | | 1961 | 50.937329805025 | | 1960 | 50.949589581586 |
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