| Year | Value | | 2022 | 8.2718038994303 | | 2021 | 6.0477459195068 | | 2020 | 4.9780967625231 | | 2019 | 5.1870835919798 | | 2018 | 4.7518030162474 | | 2017 | 4.447699373763 | | 2016 | 6.5965049069654 | | 2015 | 3.2184451365593 | | 2014 | 5.3702896100859 | | 2013 | 4.8651189949638 | | 2012 | 6.0514366213997 | | 2011 | 5.0366305210156 | | 2010 | -2.4052425459871 | | 2009 | -16.859691054064 | | 2008 | 10.715666130968 | | 2007 | 8.0124366904341 | | 2006 | 6.0727187973429 | | 2005 | 3.4378842305744 | | 2004 | 5.0234206861628 | | 2003 | 6.6291635714676 | | 2002 | 33.812578338126 | | 2001 | -9.6161535385847 | | 2000 | 6.131975387227 | | 1996 | 9.3303145853193 | | 1995 | 9.2708333333332 | | 1994 | 8.214738621953 | | 1993 | 13.135660768372 | | 1992 | 17.208520179372 | | 1991 | 17.678100263852 | | 1990 | 11.634756995582 | | 1989 | 14.72824556463 | | 1988 | 11.456371625863 | | 1987 | 11.750263065591 | | 1986 | 18.004966887417 | | 1985 | 13.320825515947 | | 1984 | 10.983862571577 | | 1983 | 17.492354740061 | | 1982 | 12.139917695473 | | 1981 | 12.413261372398 | | 1980 | 16.274841618253 | | 1979 | 16.003552397748 | | 1978 | 13.483579011849 | | 1977 | 16.688311688555 | | 1976 | 11.412551998414 | | 1975 | 14.211939681943 | | 1974 | 13.422834516592 |
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