| Year | Value | | 2014 | 36.2454955766 | | 2013 | 33.716863660216 | | 2012 | 28.737413551392 | | 2011 | 29.503421102919 | | 2010 | 29.122132826463 | | 2009 | 29.790611666431 | | 2008 | 39.513192866976 | | 2007 | 38.423485816747 | | 2006 | 37.036208143465 | | 2005 | 33.93342241796 | | 2004 | 36.377598654285 | | 2003 | 32.363175451285 | | 2002 | 36.018490401782 | | 2001 | 39.250670265305 | | 2000 | 41.151283915292 | | 1999 | 38.237333416727 | | 1998 | 43.622042556443 | | 1997 | 41.881822130677 | | 1996 | 37.299144185137 | | 1995 | 40.275783466565 | | 1994 | 38.208179233521 | | 1993 | 47.549518096912 | | 1992 | 60.046355708986 | | 1991 | 63.837240099213 | | 1990 | 61.835542367293 |
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