| Year | Value | | 2022 | 8.1605903199179 | | 2021 | 5.8122511878777 | | 2020 | 4.2017931219053 | | 2019 | 5.6105144149239 | | 2018 | 8.5942295887044 | | 2017 | 8.6090507542295 | | 2016 | 6.0357585815468 | | 2015 | 7.4041917420214 | | 2014 | 6.0804081108828 | | 2013 | 5.82642944452 | | 2012 | 5.7138443419105 | | 2011 | 9.4825404858299 | | 2010 | 9.2473217364411 | | 2009 | 8.9542180239295 | | 2008 | 9.2965083938107 | | 2007 | 10.287966318767 | | 2006 | 10.765637155486 | | 2005 | 18.363824646893 | | 2004 | 13.955801803321 | | 2003 | -1.7040047961631 | | 2002 | 16.498525531585 | | 2001 | 7.916944845296 | | 2000 | 11.859684500028 | | 1999 | 9.9295339934878 | | 1998 | 6.2080160866332 | | 1997 | 4.486382617374 | | 1996 | 19.756354543978 | | 1995 | 49.080210059078 | | 1994 | 38.941790898924 | | 1993 | 10.008361204014 | | 1992 | 14.512378607577 | | 1991 | 8.5926476049019 | | 1990 | 11.784483832136 | | 1989 | 9.012995945555 | | 1988 | 26.853797141381 | | 1987 | 14.99313513225 | | 1986 | 14.497332103913 | | 1985 | 10.556483957362 | | 1984 | 9.8566209543388 | | 1983 | 19.328338591095 | | 1982 | 31.789704651054 | | 1981 | 30.538177432771 | | 1980 | 18.217865894676 | | 1979 | 14.055592255552 | | 1978 | 6.528446922618 | | 1977 | 3.1089528912843 | | 1976 | 4.9868151186257 | | 1975 | 8.1912128321593 | | 1974 | 22.100944418778 | | 1973 | 6.1201018646478 | | 1972 | 5.6225596527748 | | 1971 | 5.385881492435 | | 1970 | 2.8786453431879 | | 1969 | 3.8288728268366 | | 1968 | 0.95651316448549 | | 1967 | 0.81519037668082 | | 1966 | 3.2115739789755 | | 1965 | 4.2018603658944 |
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