| Year | Value | | 2021 | 7.6528278331962 | | 2020 | -5.3472954399826 | | 2019 | 3.8234049742198 | | 2018 | 1.9038361809966 | | 2017 | 1.5846358403228 | | 2016 | 2.5786695388582 | | 2015 | 4.2535409803282 | | 2014 | 5.3364984378394 | | 2013 | 6.579990716564 | | 2012 | 6.0797337611383 | | 2011 | 4.8362091331321 | | 2010 | 4.767733687717 | | 2009 | 4.3475564006405 | | 2008 | 4.1093001970593 | | 2007 | 8.7683089403187 | | 2006 | 6.2793082358334 | | 2005 | 5.3752105022508 | | 2004 | 5.6244580778141 | | 2003 | 2.5217407135142 | | 2002 | 2.0873281579526 | | 2001 | 2.1817929171439 | | 2000 | 0.24295194111576 | | 1999 | -6.6680411731838 | | 1998 | 0.64756373177157 | | 1997 | 4.0419749914734 | | 1996 | 0.3989854276353 | | 1995 | 4.3733777829006 | | 1994 | 12.439236928653 | | 1993 | 6.9913816628102 | | 1992 | 5.7030207574875 | | 1991 | 4.6906728407644 | | 1990 | 1.470232509211 | | 1989 | 0.013058503397517 | | 1988 | 5.8537252151701 | | 1987 | -1.2287924888196 | | 1986 | 10.325502248057 | | 1985 | 0.94268544814436 | | 1984 | 2.4094264280179 | | 1983 | 0.79927737479186 | | 1982 | 0.97870896542037 | | 1981 | 0.17587341372915 | | 1980 | 5.2753057062906 | | 1979 | 2.4163822959444 | | 1978 | 8.6637742782646 | | 1977 | 8.9627872585967 | | 1976 | 9.8469706413843 | | 1975 | 2.4761604281865 |
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