Year Percent 1996-01-01 42.517500000000000 1997-01-01 49.986500000000000 1998-01-01 49.268600000000000 1999-01-01 55.175500000000000 2000-01-01 60.334900000000000 2001-01-01 48.237400000000000 2002-01-01 42.099300000000000 2003-01-01 37.622400000000000 2004-01-01 37.137500000000000 2005-01-01 36.072300000000000 2006-01-01 44.800400000000000 2007-01-01 36.554000000000000 2008-01-01 28.677800000000000 2009-01-01 28.431700000000000 2010-01-01 29.279200000000000 2011-01-01 30.956999999999997 2012-01-01 24.390800000000000 2013-01-01 21.312600000000000 2014-01-01 22.468300000000000 2015-01-01 21.865800000000000 2016-01-01 18.640500000000000