| Year | Value | | 2014 | 8.1047258362391 | | 2013 | 10.96844215002 | | 2012 | 9.8853871448487 | | 2011 | 19.543561713114 | | 2010 | 11.174833860504 | | 2009 | 5.4077609807752 | | 2008 | 18.976257431808 | | 2007 | 7.9051177898873 | | 2006 | 10.844798691426 | | 2005 | 11.811263937495 | | 2004 | 12.515095149521 | | 2003 | 10.832360702324 | | 2002 | 12.238533938971 | | 2001 | 11.911591292986 | | 2000 | 4.5899999999998 | | 1999 | 8.6602194936435 | | 1998 | 5.9765085214186 | | 1997 | 2.1767266737265 | | 1996 | 30.733733271804 | | 1995 | 55.081106870229 | | 1994 | 49.394155381325 | | 1993 | 35.752298016449 | | 1992 | 29.411764705882 | | 1991 | 36 |
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