Year Percent 1980-01-01 0.19414700000000001 1981-01-01 0.17975100000000000 1982-01-01 0.16892100000000002 1983-01-01 0.17397900000000000 1984-01-01 0.17308600000000000 1985-01-01 0.05762500000000000 1986-01-01 0.12270299999999999 1987-01-01 0.22365800000000000 1988-01-01 0.16369200000000000 1989-01-01 0.15220400000000000 1990-01-01 0.15055400000000000 1991-01-01 0.47416300000000000 1992-01-01 0.37406600000000000 1993-01-01 0.90736200000000010 1994-01-01 0.99519000000000000 1995-01-01 1.32704000000000000 1996-01-01 2.64460000000000000 1997-01-01 3.31150999999999970 1998-01-01 4.84353000000000000 1999-01-01 7.01493999999999900 2000-01-01 8.52007000000000000 2001-01-01 11.83640000000000000 2002-01-01 12.19720000000000000 2003-01-01 13.11580000000000000 2004-01-01 11.25310000000000000 2005-01-01 9.29162000000000000 2006-01-01 9.49750000000000000 2007-01-01 8.93250000000000000 2008-01-01 7.18375000000000000 2009-01-01 9.89597000000000000 2010-01-01 8.43256000000000000 2011-01-01 8.52955000000000000 2012-01-01 8.98913999999999900 2013-01-01 10.80390000000000000 2014-01-01 12.20510000000000000 2015-01-01 16.94780000000000000 2016-01-01 18.48600000000000000