| Year | Value | | 2017 | 4.0477746933822 | | 2016 | 3.3662351286019 | | 2015 | 9.9793531683357 | | 2014 | 3.9332700365997 | | 2013 | 5.8801186413145 | | 2012 | 5.2679659309026 | | 2011 | 5.4956122459131 | | 2010 | 1.0710513827742 | | 2009 | 4.9905426864473 | | 2008 | 1.9291616768672 | | 2007 | 1.5737845199669 | | 2006 | 2.5221098571869 | | 2005 | 2.9357666956824 | | 2004 | 1.8449955844452 | | 2003 | 1.1391651064026 | | 2002 | 2.4401897408732 | | 2001 | 3.8327366702652 | | 2000 | 10.568895833091 | | 1999 | 2.7277923737863 | | 1998 | 0.21589062942175 | | 1997 | 4.8566243327507 | | 1996 | -2.364509629904 | | 1995 | 5.9582294235681 | | 1994 | -6.8355787595486 | | 1993 | 2.170201461394 | | 1992 | 9.6239085576191 | | 1991 | -5.1697735438104 | | 1990 | 3.9363175115973 | | 1989 | -2.3119191691145 | | 1988 | 2.3643971622402 | | 1987 | 1.5742562393781 | | 1986 | 1.7619967400603 | | 1985 | 0.96621781049112 | | 1984 | 4.8180788402368 | | 1983 | 3.9378424756014 | | 1982 | 6.8531813578775 | | 1981 | 2.95129645279 |
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