| Year | Value | | 2022 | 50.264717396558 | | 2021 | 50.277675840985 | | 2020 | 50.294819639552 | | 2019 | 50.308140757882 | | 2018 | 50.315310894417 | | 2017 | 50.320192250497 | | 2016 | 50.32387802911 | | 2015 | 50.324305536784 | | 2014 | 50.321524162471 | | 2013 | 50.318726637661 | | 2012 | 50.31556859109 | | 2011 | 50.311661486066 | | 2010 | 50.309321602808 | | 2009 | 50.308143918783 | | 2008 | 50.305172870682 | | 2007 | 50.300163971433 | | 2006 | 50.294304800314 | | 2005 | 50.289729744163 | | 2004 | 50.286616188649 | | 2003 | 50.283952684361 | | 2002 | 50.281013448281 | | 2001 | 50.277673308033 | | 2000 | 50.271460108108 | | 1999 | 50.263106973257 | | 1998 | 50.255820213419 | | 1997 | 50.247994767118 | | 1996 | 50.240696539373 | | 1995 | 50.235389831808 | | 1994 | 50.229644511029 | | 1993 | 50.223385969071 | | 1992 | 50.217100727645 | | 1991 | 50.207682966627 | | 1990 | 50.196304669852 | | 1989 | 50.184145842953 | | 1988 | 50.172880573533 | | 1987 | 50.162847608748 | | 1986 | 50.15243900544 | | 1985 | 50.146976389862 | | 1984 | 50.146214414628 | | 1983 | 50.145420551538 | | 1982 | 50.143572084759 | | 1981 | 50.138862522487 | | 1980 | 50.13004494478 | | 1979 | 50.123374602507 | | 1978 | 50.120558606545 | | 1977 | 50.115784005247 | | 1976 | 50.11053250165 | | 1975 | 50.104451521227 | | 1974 | 50.093426713131 | | 1973 | 50.078629877599 | | 1972 | 50.062607755334 | | 1971 | 50.049288091904 | | 1970 | 50.039305135624 | | 1969 | 50.028625722788 | | 1968 | 50.018802823747 | | 1967 | 50.012501034224 | | 1966 | 50.008918822671 | | 1965 | 50.004472158809 | | 1964 | 49.997739874742 | | 1963 | 49.987173186246 | | 1962 | 49.976150079264 | | 1961 | 49.970637010183 | | 1960 | 49.971054551306 |
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