| Year | Value | | 2019 | 57.961660431003 | | 2018 | 55.381794111353 | | 2017 | 56.157517748345 | | 2012 | 36.508880802181 | | 2011 | 35.520419057182 | | 2010 | 36.787376159659 | | 2009 | 36.556471846337 | | 2008 | 33.698874949869 | | 2007 | 34.69344973375 | | 2006 | 38.028895768834 | | 2005 | 41.692694830242 | | 2004 | 39.063369937191 | | 2003 | 44.73734798475 | | 2002 | 39.817493816674 | | 2001 | 30.195287800623 | | 2000 | 32.117443312112 | | 1999 | 31.410472242305 | | 1998 | 33.595056606921 | | 1997 | 35.823559177421 | | 1996 | 35.750676350313 | | 1995 | 32.868605943031 | | 1994 | 31.162544538668 | | 1993 | 30.225764789803 | | 1992 | 31.956009049652 | | 1991 | 39.924941146425 | | 1990 | 39.650354969574 |
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