| Year | Value | | 2021 | 4.9549577705407 | | 2020 | 2.5440426607366 | | 2019 | 4.1804870819847 | | 2018 | 4.570732553927 | | 2017 | 8.3995417104832 | | 2016 | 8.25380221427 | | 2015 | 8.37926066158 | | 2014 | 9.2060817907209 | | 2013 | 6.062014257675 | | 2012 | 1.0084945883623 | | 2011 | -1.6063358261632 | | 2010 | 4.1901991912999 | | 2009 | 7.8061964690261 | | 2008 | 0.062764905210486 | | 2007 | 3.6936756924951 | | 2006 | 2.5918313992443 | | 2005 | 6.3197534231832 | | 2004 | 1.686315463124 | | 2003 | 8.9503044934867 | | 2002 | -2.8758751867134 | | 2001 | 10.530482270831 | | 2000 | 0.30820240501951 | | 1999 | 12.734927069494 | | 1998 | 3.5399306032505 | | 1997 | 6.5202715814203 | | 1996 | 1.1239412131336 | | 1995 | 8.6778944832629 | | 1994 | -11.250167455445 | | 1993 | 0.82962403296644 | | 1992 | 1.9252416833746 | | 1991 | 2.7043711734725 | | 1990 | 1.4650101669238 | | 1989 | 0.58783196759811 | | 1988 | -4.9857129011228 | | 1987 | 6.7306859556976 | | 1986 | 6.0308310189394 | | 1985 | 10.285074107404 | | 1984 | 9.5716953538546 | | 1983 | -7.4629099493761 | | 1982 | -2.1839826373546 | | 1981 | 8.7860055624151 | | 1980 | -1.8875715382315 | | 1979 | 5.1422052875617 | | 1978 | -3.4400878264432 | | 1977 | 0.019222802823421 | | 1976 | 6.6839149738637 | | 1975 | 3.9847225535344 | | 1974 | 8.5558801901164 | | 1973 | -7.4234546609163 | | 1972 | 6.0416671835735 |
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