| Year | Value | | 2022 | 52.392269256343 | | 2021 | 51.904449372969 | | 2020 | 51.400155078544 | | 2019 | 50.889175353713 | | 2018 | 50.36594727302 | | 2017 | 49.834653244403 | | 2016 | 49.296257939365 | | 2015 | 48.752579628024 | | 2014 | 48.201488104229 | | 2013 | 47.655465291694 | | 2012 | 47.117094816708 | | 2011 | 46.586706305425 | | 2010 | 46.046834513979 | | 2009 | 45.479963793235 | | 2008 | 44.910063692717 | | 2007 | 44.339016023096 | | 2006 | 43.783768999003 | | 2005 | 43.216726121345 | | 2004 | 42.641079967449 | | 2003 | 42.071926545845 | | 2002 | 41.511810520947 | | 2001 | 40.956720252395 | | 2000 | 40.441170578091 | | 1999 | 39.975873123541 | | 1998 | 39.518515522061 | | 1997 | 39.061494806169 | | 1996 | 38.61113910605 | | 1995 | 38.168007624176 | | 1994 | 37.720307855323 | | 1993 | 37.270654408442 | | 1992 | 36.825476059082 | | 1991 | 36.376749115994 | | 1990 | 35.918634273991 | | 1989 | 35.462610454098 | | 1988 | 34.993566998355 | | 1987 | 34.508212091048 | | 1986 | 34.0204042236 | | 1985 | 33.527392264511 | | 1984 | 33.032359679715 | | 1983 | 32.539515919353 | | 1982 | 32.063811979856 | | 1981 | 31.548792735698 | | 1980 | 30.993648045538 | | 1979 | 30.445073034881 | | 1978 | 29.908541748443 | | 1977 | 29.453136584671 | | 1976 | 29.082181156558 | | 1975 | 28.715874169769 | | 1974 | 28.405641598533 | | 1973 | 28.052625811391 | | 1972 | 27.737388930528 | | 1971 | 27.453120358529 | | 1970 | 27.203177279809 | | 1969 | 26.973914104582 | | 1968 | 26.740816903819 | | 1967 | 26.501515331839 | | 1966 | 26.260058613848 | | 1965 | 26.033123022823 | | 1964 | 25.798803107178 | | 1963 | 25.349151636638 | | 1962 | 24.907214409594 | | 1961 | 24.435451130459 | | 1960 | 23.936638709103 |
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