| Year | Value | | 2022 | 0.73634922289667 | | 2021 | 0.6970877404099 | | 2020 | 0.73233855162766 | | 2019 | 0.70682320579403 | | 2018 | 0.72708462543398 | | 2017 | 0.6482294923693 | | 2016 | 0.59932388341049 | | 2015 | 0.65811880076494 | | 2014 | 0.63713109515615 | | 2013 | 0.50398981754815 | | 2012 | 0.46131140882161 | | 2011 | 0.51910922770959 | | 2010 | 0.53173667122248 | | 2009 | 0.61296366150853 | | 2008 | 0.85192806429066 | | 2007 | 1.1850163712649 | | 2006 | 1.4070834263145 | | 2005 | 1.4597280331678 | | 2004 | 1.4931307653712 | | 2003 | 1.5454731222705 | | 2002 | 1.5901195818369 | | 2001 | 1.629362338419 | | 2000 | 1.6498682624854 | | 1999 | 1.6087648859896 | | 1998 | 1.5961560489092 | | 1997 | 1.6224721980074 | | 1996 | 1.6042861245761 | | 1995 | 1.6396666415969 | | 1994 | 1.7581468206158 | | 1993 | 1.8465116876841 | | 1992 | 1.9202318493297 | | 1991 | 2.0421169494353 | | 1990 | 2.1635666518473 | | 1989 | 2.3664439345758 | | 1988 | 2.450724264049 | | 1987 | 2.3956812321099 | | 1986 | 2.4320925758645 | | 1985 | 2.3911109941969 | | 1984 | 2.2663233775149 | | 1983 | 2.6595791998998 | | 1982 | 3.1765165803271 | | 1981 | 3.1890046956589 | | 1980 | 3.1217419745245 | | 1979 | 3.0856604852608 | | 1978 | 3.1302101124915 | | 1977 | 3.1710813823523 | | 1976 | 3.1833617438105 | | 1975 | 3.2592225665745 | | 1974 | 3.355283342821 | | 1973 | 3.4401464919391 | | 1972 | 3.4996430396904 | | 1971 | 3.5145430284102 | | 1970 | 3.5291585368309 | | 1969 | 3.5516957788119 | | 1968 | 3.5560002407088 | | 1967 | 3.5667995730507 | | 1966 | 3.590244023935 | | 1965 | 3.5925582565507 | | 1964 | 3.4509582410473 | | 1963 | 3.0415600579318 | | 1962 | 2.5971061508982 | | 1961 | 2.4102883039461 |
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