| Year | Value | | 2022 | 49.675080959735 | | 2021 | 49.68091491502 | | 2020 | 49.686829595125 | | 2019 | 49.695871362577 | | 2018 | 49.714508948819 | | 2017 | 49.736502894788 | | 2016 | 49.762541605933 | | 2015 | 49.795009727169 | | 2014 | 49.834885594501 | | 2013 | 49.883452690986 | | 2012 | 49.940890218695 | | 2011 | 50.005080400713 | | 2010 | 50.077350707755 | | 2009 | 50.161462743466 | | 2008 | 50.252210795171 | | 2007 | 50.341515924774 | | 2006 | 50.428194904736 | | 2005 | 50.51291320935 | | 2004 | 50.59533576702 | | 2003 | 50.67670369631 | | 2002 | 50.758320970443 | | 2001 | 50.841622703747 | | 2000 | 50.907126066356 | | 1999 | 50.875433087786 | | 1998 | 50.780429134917 | | 1997 | 50.713634258499 | | 1996 | 50.710815826098 | | 1995 | 50.763255232732 | | 1994 | 50.808090223403 | | 1993 | 50.795235095419 | | 1992 | 50.77226650788 | | 1991 | 50.815109894955 | | 1990 | 50.897254635594 | | 1989 | 50.974292654795 | | 1988 | 50.908918004243 | | 1987 | 50.696996720574 | | 1986 | 50.473325759788 | | 1985 | 50.257027102531 | | 1984 | 50.165172719909 | | 1983 | 50.197273567069 | | 1982 | 50.231437553694 | | 1981 | 50.26707957349 | | 1980 | 50.303870646434 | | 1979 | 50.341166664378 | | 1978 | 50.380109132415 | | 1977 | 50.421170885307 | | 1976 | 50.46287451199 | | 1975 | 50.505452848476 | | 1974 | 50.547522942733 | | 1973 | 50.589033610202 | | 1972 | 50.627754907229 | | 1971 | 50.663472415886 | | 1970 | 50.69867581863 | | 1969 | 50.733554172038 | | 1968 | 50.769695065072 | | 1967 | 50.806402601292 | | 1966 | 50.842438052553 | | 1965 | 50.880728993281 | | 1964 | 50.920690137405 | | 1963 | 50.960669822042 | | 1962 | 51.001298104523 | | 1961 | 51.042605476566 | | 1960 | 51.083587555676 |
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