Year Percent 1980-01-01 0.5960000000000000 1981-01-01 0.7223590000000000 1982-01-01 1.1222400000000000 1983-01-01 1.2038600000000000 1984-01-01 1.4450200000000000 1985-01-01 1.9596099999999999 1986-01-01 2.6201800000000000 1987-01-01 3.0217500000000000 1988-01-01 2.9322200000000000 1989-01-01 2.6837400000000002 1990-01-01 2.6243900000000000 1991-01-01 2.6250700000000000 1992-01-01 2.4334599999999997 1993-01-01 2.3233099999999998 1994-01-01 2.5706599999999997 1995-01-01 3.2379700000000002 1996-01-01 4.1303300000000010 1997-01-01 4.8828900000000000 1998-01-01 6.4093700000000000 1999-01-01 8.2287000000000000 2000-01-01 10.3171000000000000 2001-01-01 14.6382000000000000 2002-01-01 16.7986000000000000 2003-01-01 18.3442000000000000 2004-01-01 18.8906000000000000 2005-01-01 17.9370000000000000 2006-01-01 20.7228000000000000 2007-01-01 23.9190000000000000 2008-01-01 23.5717000000000000 2009-01-01 23.5424000000000000 2010-01-01 21.5720000000000000 2011-01-01 19.3405000000000000 2012-01-01 18.3214000000000000 2013-01-01 17.8301000000000000 2014-01-01 17.5504000000000000 2015-01-01 17.6112000000000000 2016-01-01 17.7240000000000000