Year Percent 1986-01-01 1.52454996722288 1987-01-01 1.91604510558446 1988-01-01 2.74651751271780 1989-01-01 3.79149955004375 1990-01-01 4.69777876058806 1991-01-01 5.50525254994482 1992-01-01 6.86853353812050 1993-01-01 5.64994293681174 1994-01-01 4.83083225777156 1995-01-01 3.36937423272806 1996-01-01 3.69746858609662 1997-01-01 4.09020542359419 1998-01-01 4.71783373025866 1999-01-01 5.10215459363612 2000-01-01 4.75328132251324 2001-01-01 3.64278252844088 2002-01-01 3.27770011659126 2003-01-01 3.61351317464974 2004-01-01 2.48957039693777 2005-01-01 1.89320791995375 2006-01-01 2.01043993757226 2007-01-01 1.44499510582316 2008-01-01 1.98807332059225 2009-01-01 3.11061717980265 2010-01-01 3.28896610564814 2011-01-01 3.01156851911543 2012-01-01 3.77710945156070 2013-01-01 3.64012662269902 2014-01-01 2.96805524860689 2015-01-01 3.32524172195668 2016-01-01 3.15450230140799 2017-01-01 2.81028120333028