| Year | Value | | 2015 | -2.7059599538985 | | 2014 | 3.3972034391434 | | 2013 | 7.2269190549618 | | 2012 | 7.7902237928253 | | 2011 | 10.445366109383 | | 2010 | 12.313255973488 | | 2009 | 14.621745406261 | | 2008 | 23.025613587711 | | 2007 | 22.522671211279 | | 2006 | 26.318939549649 | | 2005 | 25.768715660362 | | 2004 | 30.067261759121 | | 2003 | 24.968829516906 | | 2002 | 28.37401733652 | | 2001 | 35.517407759845 | | 2000 | 32.531254659908 | | 1999 | 37.847041113265 | | 1998 | 36.685699938873 | | 1997 | 30.799350912288 | | 1996 | 30.684770243919 | | 1995 | 34.531814116472 | | 1994 | 34.647705259498 | | 1993 | 35.318326285408 | | 1992 | 32.246128514673 | | 1991 | 46.883236141134 | | 1990 | 44.636742591517 |
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