| Year | Value | | 2018 | 4.3557233196425 | | 2017 | 6.0726904388423 | | 2016 | 5.8773630939976 | | 2015 | 11.223523017688 | | 2014 | 0.61707329117271 | | 2013 | 3.9338881464666 | | 2012 | 10.881615089298 | | 2011 | 1.9536877801285 | | 2010 | 3.2161608906187 | | 2009 | 9.8533778675085 | | 2008 | -1.5044628782813 | | 2007 | 7.3364707480291 | | 2006 | 8.0094354886095 | | 2005 | 15.353576097452 | | 2004 | 6.5873177153062 | | 2003 | 6.7556309081341 | | 2002 | 4.2001739872375 | | 2001 | 1.4898836473422 | | 2000 | 1.3279678495246 | | 1999 | 2.4180286821496 | | 1998 | 0.66530285710738 | | 1997 | 6.0407461224864 | | 1996 | 3.7375572973996 | | 1995 | 6.0172784010864 | | 1994 | 5.4172751248008 | | 1993 | 12.111576469772 | | 1992 | 5.1437104863729 | | 1991 | 11.681514043822 | | 1990 | 8.7039413602983 | | 1989 | 14.392491748571 | | 1988 | 8.5643589271143 | | 1987 | 14.195366262895 | | 1986 | 8.6345561730031 | | 1985 | 10.263661452535 |
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