Year Percent 1999-01-01 52.050 2000-01-01 53.100 2001-01-01 52.600 2002-01-01 52.600 2003-01-01 52.425 2004-01-01 53.125 2005-01-01 53.900 2006-01-01 54.000 2007-01-01 55.125 2008-01-01 55.550 2009-01-01 54.900 2010-01-01 55.275 2011-01-01 55.150 2012-01-01 54.975 2013-01-01 54.775 2014-01-01 54.775 2015-01-01 54.575 2016-01-01 54.750 2017-01-01 55.400