Year Percent 1999-01-01 2.3675200000000003 2000-01-01 2.2482400000000000 2001-01-01 2.2677099999999997 2002-01-01 2.3002200000000000 2003-01-01 2.3613800000000000 2004-01-01 2.3145100000000000 2005-01-01 2.2510700000000000 2006-01-01 2.2216099999999996 2007-01-01 2.1768300000000000 2008-01-01 2.1902100000000000 2009-01-01 2.2366700000000000 2010-01-01 2.1846900000000002 2011-01-01 2.2119600000000000 2012-01-01 2.2527700000000000 2013-01-01 2.2680200000000000 2014-01-01 2.2019900000000003 2015-01-01 2.1386600000000000