| Year | Value | | 2022 | 49.502907928586 | | 2021 | 49.454912998502 | | 2020 | 49.398941921913 | | 2019 | 49.340541286014 | | 2018 | 49.281861182724 | | 2017 | 49.22312664118 | | 2016 | 49.164030122399 | | 2015 | 49.104424872659 | | 2014 | 49.049210958902 | | 2013 | 49.001818627677 | | 2012 | 48.959701893741 | | 2011 | 48.923487849255 | | 2010 | 48.893649488069 | | 2009 | 48.870787387381 | | 2008 | 48.853443291028 | | 2007 | 48.837961405466 | | 2006 | 48.822353876159 | | 2005 | 48.805691817869 | | 2004 | 48.78774124773 | | 2003 | 48.768875169474 | | 2002 | 48.746994880493 | | 2001 | 48.720941122352 | | 2000 | 48.692597557955 | | 1999 | 48.662487764226 | | 1998 | 48.631858147862 | | 1997 | 48.601256044662 | | 1996 | 48.569069891782 | | 1995 | 48.535339962376 | | 1994 | 48.502161819208 | | 1993 | 48.471876910765 | | 1992 | 48.437739549424 | | 1991 | 48.396303877515 | | 1990 | 48.352983864101 | | 1989 | 48.308133241506 | | 1988 | 48.260974744156 | | 1987 | 48.211332325792 | | 1986 | 48.159290773821 | | 1985 | 48.104800670741 | | 1984 | 48.048437938596 | | 1983 | 47.990457592238 | | 1982 | 47.930517243812 | | 1981 | 47.868255037701 | | 1980 | 47.804235644958 | | 1979 | 47.738624581329 | | 1978 | 47.671412482099 | | 1977 | 47.602337803412 | | 1976 | 47.529818092125 | | 1975 | 47.450998167103 | | 1974 | 47.364488974328 | | 1973 | 47.26888846699 | | 1972 | 47.155712993162 | | 1971 | 47.028909687441 | | 1970 | 46.895817456419 | | 1969 | 46.753160679885 | | 1968 | 46.60291123467 | | 1967 | 46.442341732308 | | 1966 | 46.278144796865 | | 1965 | 46.119105023018 | | 1964 | 45.959714011854 | | 1963 | 45.794171749536 | | 1962 | 45.627262580657 | | 1961 | 45.465792641557 | | 1960 | 45.296613681277 |
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