| Year | Value | | 2021 | 8.2976678572954 | | 2020 | 2.7307025571718 | | 2019 | 7.9776502733909 | | 2018 | 6.2651640020407 | | 2017 | 3.7140832133803 | | 2016 | 4.4812701408195 | | 2015 | 3.1518085993985 | | 2014 | 6.2017803903191 | | 2013 | 9.8499489701273 | | 2012 | 6.1652777906976 | | 2011 | 4.741783056646 | | 2010 | 1.9406073487615 | | 2009 | 2.3432479884343 | | 2008 | 5.2586591833771 | | 2007 | 5.5361247527683 | | 2006 | 3.8388677622401 | | 2005 | 0.57945429565804 | | 2004 | 6.5674150050141 | | 2003 | 5.0594471336824 | | 2002 | 8.2332498809975 | | 2001 | 7.4306812486119 | | 2000 | 8.7772229395403 | | 1999 | 10.610065204254 | | 1998 | 4.2356079053709 | | 1997 | 7.4299540171164 | | 1996 | 6.377935240515 | | 1995 | 6.0291440528697 | | 1994 | -9.1655853135178 | | 1993 | 9.3231391796131 | | 1992 | -3.6178333705968 | | 1991 | 5.6270313502784 | | 1990 | 10.49676705054 | | 1989 | -6.2140609962994 | | 1988 | 4.4702442162522 | | 1987 | -2.0604929805574 | | 1986 | -1.2544996359899 | | 1985 | 9.6561990198219 | | 1984 | 5.7000653207106 | | 1983 | -4.6303808356991 | | 1982 | -4.6192431960187 | | 1981 | 5.0725754891227 | | 1980 | 8.4913483732226 | | 1979 | 11.724497457459 | | 1978 | 3.835627051666 | | 1977 | 0.65230740858367 | | 1976 | 0.52277541827019 | | 1975 | -6.9961902544504 | | 1974 | 0.53819079055904 | | 1973 | 4.1058563950505 | | 1972 | 6.0242834798764 |
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