Year Percent 1998-01-01 16.5000 1999-01-01 14.9000 2000-01-01 13.7000 2001-01-01 13.8000 2002-01-01 13.0000 2003-01-01 11.8000 2004-01-01 12.4000 2005-01-01 11.6000 2006-01-01 11.0000 2007-01-01 10.4000 2008-01-01 12.3000 2009-01-01 13.9000 2010-01-01 13.8917 2011-01-01 13.8152 2012-01-01 16.3120 2013-01-01 17.4150 2014-01-01 16.9222 2015-01-01 16.9492 2016-01-01 17.9739