| Year | Value | | 2013 | -26.164858471612 | | 2012 | -17.496116331106 | | 2011 | -21.036311396711 | | 2010 | -27.592797034322 | | 2009 | -28.470901542396 | | 2008 | -24.897822521202 | | 2007 | -25.481978757192 | | 2006 | -21.876167587209 | | 2005 | -20.069186390064 | | 2004 | -14.332274955217 | | 2003 | -9.7060285088606 | | 2002 | -5.7426963983033 | | 2001 | -8.7320330032511 | | 2000 | -8.2893213943759 | | 1999 | -7.5117826276483 | | 1998 | -9.1396152453409 | | 1997 | -14.386736787865 | | 1996 | -11.320838593708 | | 1995 | -14.098775347208 | | 1994 | 0.82177894711651 | | 1993 | 8.8720163171524 | | 1992 | 9.9546414876251 | | 1991 | 17.56197412479 | | 1990 | 16.654662783844 |
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