| Year | Value | | 2017 | 12.954256319487 | | 2016 | 11.693842102314 | | 2015 | 17.21042350692 | | 2014 | 16.727878373761 | | 2013 | 11.489574058347 | | 2012 | 11.055834919455 | | 2011 | 11.433876739772 | | 2010 | 11.425493500339 | | 2009 | 10.700213487174 | | 2008 | 10.297397955575 | | 2007 | 18.860179834191 | | 2006 | 35.442053445798 | | 2005 | 36.667659571713 | | 2004 | 38.260176072437 | | 2003 | 39.661030631265 | | 2002 | 37.93937616831 | | 2001 | 37.447116777746 | | 2000 | 35.62478582161 | | 1999 | 49.33577645442 | | 1998 | 47.191011235955 | | 1997 | 50.750906266183 | | 1996 | 47.928331466965 | | 1995 | 51.585365853659 | | 1994 | 49.061488673139 | | 1993 | 51.03734439834 | | 1992 | 47.656813266042 | | 1991 | 48.775055679287 | | 1990 | 49.198312236287 |
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