| Year | Value | | 2022 | 49.959364845182 | | 2021 | 49.967227038968 | | 2020 | 49.975509039732 | | 2019 | 49.979246108524 | | 2018 | 49.97668074307 | | 2017 | 49.97528930514 | | 2016 | 49.977582833671 | | 2015 | 49.986133826043 | | 2014 | 49.996429808022 | | 2013 | 50.005493400477 | | 2012 | 50.01687452596 | | 2011 | 50.030883637516 | | 2010 | 50.044996847198 | | 2009 | 50.05757984584 | | 2008 | 50.067111939671 | | 2007 | 50.072765578249 | | 2006 | 50.075179693524 | | 2005 | 50.07372215465 | | 2004 | 50.063192485833 | | 2003 | 50.046221123957 | | 2002 | 50.028241884075 | | 2001 | 50.008790640374 | | 2000 | 49.983097667558 | | 1999 | 49.952866977082 | | 1998 | 49.927581057251 | | 1997 | 49.907432958574 | | 1996 | 49.889384292783 | | 1995 | 49.87558957824 | | 1994 | 49.868640141616 | | 1993 | 49.867671337003 | | 1992 | 49.883788032113 | | 1991 | 49.916737463785 | | 1990 | 49.952612116176 | | 1989 | 49.989310001113 | | 1988 | 50.027331593608 | | 1987 | 50.068773303378 | | 1986 | 50.113949304332 | | 1985 | 50.160804831879 | | 1984 | 50.20722545015 | | 1983 | 50.25376239072 | | 1982 | 50.300493384091 | | 1981 | 50.346738744642 | | 1980 | 50.392725863069 | | 1979 | 50.437251151382 | | 1978 | 50.481374478581 | | 1977 | 50.527566082116 | | 1976 | 50.575377198242 | | 1975 | 50.626790881212 | | 1974 | 50.68029244939 | | 1973 | 50.734677517301 | | 1972 | 50.78840879644 | | 1971 | 50.839822087417 | | 1970 | 50.891943052915 | | 1969 | 50.944540459935 | | 1968 | 50.999591532287 | | 1967 | 51.058504348606 | | 1966 | 51.120893360085 | | 1965 | 51.18907066626 | | 1964 | 51.258881424926 | | 1963 | 51.328307319065 | | 1962 | 51.401868641863 | | 1961 | 51.480007933688 | | 1960 | 51.557724026258 |
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