| Year | Value | | 2021 | 4.9290328971082 | | 2020 | -9.0790761146302 | | 2019 | 2.7435202583999 | | 2018 | 2.0853365822968 | | 2017 | 3.1948640832796 | | 2016 | 3.0044004593693 | | 2015 | 2.5273154797802 | | 2014 | 0.12642749357481 | | 2013 | 1.7160382217464 | | 2012 | -4.9880661182486 | | 2011 | -1.1935533586281 | | 2010 | 1.1491164561105 | | 2009 | -1.5127081671073 | | 2008 | -2.0595460765293 | | 2007 | 2.8871052308547 | | 2006 | 0.20402857557372 | | 2005 | 0.24461152085247 | | 2004 | 1.2251417834895 | | 2003 | 0.19964239701912 | | 2002 | 1.7019915659069 | | 2001 | 1.969167208509 | | 2000 | 0.50816883094133 | | 1999 | 4.3269989141555 | | 1998 | 5.8712217746636 | | 1997 | 3.8639927500376 | | 1996 | 2.7756500263672 | | 1995 | 1.3292442615639 | | 1994 | 3.1525478247759 | | 1993 | -1.0165981106309 | | 1992 | 4.4139694244746 | | 1991 | 4.3771946099329 | | 1990 | 7.259360491721 | | 1989 | 6.5522031170095 | | 1988 | 7.4350217838421 | | 1987 | 6.7475313345298 | | 1986 | 11.779856814894 | | 1985 | 6.0897417158923 | | 1984 | -2.2283804251652 | | 1983 | 1.4197005875374 | | 1982 | 0.1486406316336 | | 1981 | -1.5737814238509 | | 1980 | 2.0175966774976 | | 1979 | 4.3065873473015 | | 1978 | 0.013538662342768 | | 1977 | 4.108215448048 | | 1976 | 6.1578725105304 | | 1975 | -6.6216684694131 | | 1974 | 0.94927803907525 | | 1973 | 13.135532555916 | | 1972 | 8.1820148755222 | | 1971 | 7.9843952014333 |
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