| Year | Value | | 2021 | 4.6824527865242 | | 2020 | -2.0076581176587 | | 2019 | 3.4693025361332 | | 2018 | 1.2943436462788 | | 2017 | 3.3306496655917 | | 2016 | 1.8518370527334 | | 2015 | 3.5531168133338 | | 2014 | 2.625898300169 | | 2013 | 1.1732814965222 | | 2012 | 0.51282470339301 | | 2011 | 2.1936373849642 | | 2010 | 6.7137160481641 | | 2009 | -6.5539919083467 | | 2008 | 0.82094580629999 | | 2007 | 4.5431197378065 | | 2006 | 6.4685214914767 | | 2005 | 2.9608842914497 | | 2004 | 2.7780871125584 | | 2003 | 4.0561209875338 | | 2002 | 1.2245469876276 | | 2001 | 0.2093528268008 | | 2000 | 3.8006915559517 | | 1999 | 4.4622005695921 | | 1998 | 4.3408220257361 | | 1997 | 2.4429668530163 | | 1996 | 0.6707317349276 | | 1995 | 5.8511853911204 | | 1994 | 6.7795198036698 | | 1993 | -4.4935840089855 | | 1992 | -2.6528377329168 | | 1991 | 0.74023415750456 | | 1990 | 0.37589000767333 | | 1989 | 1.7357460929657 | | 1988 | 2.159995457599 | | 1987 | 3.2436615520357 | | 1986 | 5.3910326702683 | | 1985 | 1.7312837384 | | 1984 | 5.3556237782259 | | 1983 | 1.023263303753 | | 1982 | 0.51945336258082 | | 1981 | 0.089528738089939 | | 1980 | 1.1100510421998 | | 1979 | 3.0811893249699 | | 1978 | 0.60970179281445 | | 1977 | -3.5366044801211 | | 1976 | 0.84831403889025 | | 1975 | 4.8899721031244 | | 1974 | 0.073788305498084 | | 1973 | 3.7471939220217 | | 1972 | 2.3854773872799 | | 1971 | 0.93333770839506 |
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