| Year | Value | | 2021 | 3.3872705281351 | | 2020 | -2.7528377536889 | | 2019 | 1.7739488745031 | | 2018 | 1.1298660043999 | | 2017 | 3.7573022659213 | | 2016 | -3.5839290272085 | | 2015 | -5.5493326107817 | | 2014 | 0.64154298801836 | | 2013 | 4.4009535166998 | | 2012 | 0.96217817388495 | | 2011 | 3.2475704800973 | | 2010 | 6.1464504313014 | | 2009 | 0.65432484473203 | | 2008 | 3.7053610777309 | | 2007 | 7.4621073909155 | | 2006 | 5.800961807645 | | 2005 | 2.4734972603217 | | 2004 | 7.0824152189916 | | 2003 | 1.3678475530679 | | 2002 | 2.7990389442193 | | 2001 | 0.23069097094992 | | 2000 | 2.9880619812425 | | 1999 | -2.6924627287047 | | 1998 | 0.57629940864066 | | 1997 | 1.7752375124284 | | 1996 | 0.35754642913864 | | 1995 | 13.385541186605 | | 1994 | 20.707813240652 | | 1993 | 4.5514338974002 | | 1992 | 0.14279223602614 | | 1991 | 2.3576773395691 | | 1990 | -11.435932634991 |
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