| Year | Value | | 2021 | 3.8562453580801 | | 2020 | -1.0599569262937 | | 2019 | 0.81060826563176 | | 2018 | 1.6597232748602 | | 2017 | 2.7738769542375 | | 2016 | 2.3845798848496 | | 2015 | 1.9934621253845 | | 2014 | 1.0301141440411 | | 2013 | 0.61373497154867 | | 2012 | -2.4313301379446 | | 2011 | 0.98688985212007 | | 2010 | 3.4193128231403 | | 2009 | -8.2104403587884 | | 2008 | -1.0322279625123 | | 2007 | 4.4712026135357 | | 2006 | 3.4076964901295 | | 2005 | 0.87168114934204 | | 2004 | 4.6807750585751 | | 2003 | 0.39071591932783 | | 2002 | 1.4006863183978 | | 2001 | 3.3575746437282 | | 2000 | 4.4181170919028 | | 1999 | 4.7314315192154 | | 1998 | 6.6260267765757 | | 1997 | 8.4084289162685 | | 1996 | 3.4095386980018 | | 1995 | 11.668175170637 | | 1994 | 7.1670655496317 | | 1993 | -1.5430427723825 | | 1992 | -5.4057742527165 | | 1991 | -9.9138268905465 | | 1990 | -2.2469226891302 | | 1989 | 2.7544873354372 | | 1988 | 6.6049796669648 | | 1987 | 3.2524130655737 | | 1986 | 4.3926045940214 | | 1985 | 2.9382970707283 | | 1984 | 4.777054368957 | | 1983 | 2.4190312580969 | | 1982 | 3.0672533832765 | | 1981 | 1.5586693892929 | | 1980 | 2.2009449168561 | | 1979 | 7.9402050468913 | | 1978 | 3.7867972709498 | | 1977 | -1.7705810167031 | | 1976 | 2.2715428673295 | | 1975 | -1.1107447916668 | | 1974 | 0.53209366823295 | | 1973 | 6.5509224828491 | | 1972 | 7.349860868438 | | 1971 | 0.92632207636912 |
|