| Year | Value | | 2022 | 2.4181017899628 | | 2021 | 2.5752385641187 | | 2020 | 2.8695775801466 | | 2019 | 2.8724017522115 | | 2018 | 2.8653298196538 | | 2017 | 3.2389940847069 | | 2016 | 3.184808543057 | | 2015 | 3.3420772536642 | | 2014 | 3.4030806974389 | | 2013 | 3.1061734806372 | | 2012 | 2.8142451056105 | | 2011 | 2.7416026358374 | | 2010 | 3.0695658571454 | | 2009 | 3.2399087711239 | | 2008 | 2.8042072694151 | | 2007 | 2.8637100889721 | | 2006 | 3.0751641209389 | | 2005 | 3.2297041030114 | | 2004 | 3.3644827582991 | | 2003 | 3.5861860267427 | | 2002 | 3.496051949906 | | 2001 | 3.5139081297369 | | 2000 | 3.2656441986014 | | 1999 | 3.4320442780147 | | 1998 | 3.666054221126 | | 1997 | 3.6303168942759 | | 1996 | 3.4938278432492 | | 1995 | 3.7368902347046 | | 1994 | 4.2737549401367 | | 1993 | 3.7993802075673 | | 1992 | 4.5778783300831 | | 1991 | 4.4954608186825 | | 1989 | 4.0571990576785 | | 1988 | 4.916658732359 | | 1987 | 5.5125400735809 | | 1986 | 5.9494685011751 | | 1985 | 6.3565815737329 | | 1984 | 6.3052761540896 | | 1983 | 6.6164841915255 | | 1982 | 7.0783609233761 | | 1981 | 7.5334246725652 | | 1980 | 5.5349719636368 | | 1979 | 5.7841487945907 | | 1978 | 8.7488060164216 | | 1977 | 9.0911817584062 | | 1976 | 9.9684633295045 | | 1975 | 10.234775938396 | | 1974 | 8.6445069373598 | | 1973 | 5.4160607134093 | | 1972 | 5.8348008791719 | | 1971 | 7.0901325313724 | | 1970 | 8.0933624509156 | | 1969 | 7.464506190162 | | 1968 | 6.8622838182154 | | 1967 | 5.7172765060598 | | 1966 | 5.4636092872451 | | 1965 | 5.4197940788005 | | 1964 | 4.3209948807995 | | 1963 | 3.6169099740343 | | 1962 | 4.4783019186328 | | 1961 | 4.0558848649501 | | 1960 | 4.0155269203124 |
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