| Year | Value | | 2019 | 0.28973476923895 | | 2018 | 0.96696049799918 | | 2017 | 1.4622321304304 | | 2016 | 3.3625828265944 | | 2015 | 5.1717881218669 | | 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 | 0.85375210843119 | | 1988 | 4.8899006453816 | | 1987 | 0.97849917463063 | | 1986 | -4.6290425931997 | | 1985 | 3.274954682106 | | 1984 | 8.0375414642602 | | 1983 | 5.605094427758 | | 1982 | 8.6363629548213 | | 1981 | 18.976670234931 | | 1980 | -5.1359912219092 | | 1979 | 0.84245644688636 | | 1978 | 6.6482851349716 | | 1977 | 8.6334973815045 | | 1976 | 5.3808037188949 | | 1975 | 8.7766801732026 |
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