| Year | Value | | 2019 | 0.29210643882432 | | 2018 | 0.9649768539313 | | 2017 | 1.4610931014878 | | 2016 | 3.3625917667492 | | 2015 | 5.1730859349614 | | 2014 | 2.841052980235 | | 2013 | 2.9418398905533 | | 2012 | 5.1563680500959 | | 2011 | 0.40657327786606 | | 2010 | 7.24243153353 | | 2009 | 3.569512290765 | | 2008 | -2.219329763542 | | 2007 | 3.3964334683256 | | 2006 | 13.863845102716 | | 2005 | 9.4938139010887 | | 2004 | 5.6919696339068 | | 2003 | 5.9891520836003 | | 2002 | 2.2831650487876 | | 2001 | 4.1852218525753 | | 2000 | 2.4987063523845 | | 1999 | 5.3323071051321 | | 1998 | 0.88897823987602 | | 1997 | 2.2219094813881 | | 1996 | 6.9078479091308 | | 1995 | -1.6081204692794 | | 1994 | 1.0443029334781 | | 1993 | -12.380145020401 | | 1992 | -16.820074395126 | | 1991 | -10.409285644077 | | 1990 | 0.39003017105965 | | 1989 | 0.8537521089474 | | 1988 | 4.889900645686 | | 1987 | 0.97849917516572 | | 1986 | -4.6290425934492 | | 1985 | 3.2749546810251 | | 1984 | 8.0375414669228 | | 1983 | 5.6050944265762 | | 1982 | 8.636362954144 | | 1981 | 18.976670234395 | | 1980 | -5.1359912215249 | | 1979 | 0.84245644650507 | | 1978 | 6.6482851361941 | | 1977 | 8.6334973824827 | | 1976 | 5.3808037156022 | | 1975 | 8.7766801762761 | | 1974 | 0.90976256200221 | | 1973 | 3.3886927743638 | | 1972 | 4.8242099510887 | | 1971 | 8.6190961264267 |
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