| Year | Value | | 2014 | 33.116297507868 | | 2013 | 31.637960448714 | | 2012 | 31.932909284183 | | 2011 | 31.576976462917 | | 2010 | 31.667496345701 | | 2009 | 29.092641860635 | | 2008 | 34.69567871951 | | 2007 | 33.429593504911 | | 2006 | 29.684071417595 | | 2005 | 27.362104176799 | | 2004 | 24.478507569345 | | 2003 | 19.574299105622 | | 2002 | 18.636542521019 | | 2001 | 21.641885466367 | | 2000 | 20.33631777112 | | 1999 | 19.513027658129 | | 1998 | 18.412993472088 | | 1997 | 18.417237409413 | | 1996 | 17.922648112514 | | 1995 | 18.024613453851 |
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