| Year | Value | | 2020 | 13.565559252501 | | 2019 | 11.552705311201 | | 2018 | 13.425805427663 | | 2017 | 8.4208566079989 | | 2016 | 7.7470492915869 | | 2015 | 10.089029696441 | | 2014 | 12.004617682093 | | 2013 | 1.0543896839795 | | 2012 | 2.1778330221647 | | 2011 | 10.860750301095 | | 2010 | -2.8931177090216 | | 2009 | 4.993121690074 | | 2008 | 9.5648887865593 | | 2007 | 9.011689212032 | | 2006 | 4.0552960192608 | | 2005 | 2.690953073419 | | 2004 | 7.8719255772089 | | 2003 | 6.4510300208744 | | 2002 | 5.7874126478359 | | 2001 | 0.91958689692291 | | 1997 | 14.44203093068 | | 1996 | 6.5702234727737 | | 1995 | 9.6726505995884 | | 1994 | 7.4511116388179 | | 1993 | 7.4068673079686 | | 1992 | 7.4689551901203 | | 1991 | 3.9157165906187 | | 1990 | 14.476643367149 | | 1989 | 6.9380969802628 | | 1988 | 14.608948231947 | | 1987 | 12.860127207335 | | 1986 | 13.830150513617 | | 1985 | -13.967934266637 | | 1984 | -3.7540349921085 | | 1983 | -10.500211857042 | | 1982 | -15.093634152533 |
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