Year Percent 1980-01-01 0.25578100000000000 1981-01-01 0.27675200000000000 1982-01-01 0.26188300000000000 1983-01-01 0.24519300000000000 1984-01-01 0.22496200000000000 1985-01-01 0.20642300000000000 1986-01-01 0.20176700000000000 1987-01-01 0.17269200000000000 1988-01-01 0.15510100000000000 1989-01-01 0.07207000000000001 1990-01-01 0.07207000000000001 1991-01-01 0.07207000000000001 1992-01-01 0.07207000000000001 1993-01-01 0.07207000000000001 1994-01-01 0.07207000000000001 1995-01-01 0.07207000000000001 1996-01-01 0.07207000000000001 1997-01-01 0.07207000000000001 1998-01-01 10.23690000000000000 1999-01-01 10.25450000000000000 2000-01-01 11.62730000000000000 2001-01-01 10.99150000000000000 2002-01-01 9.74957000000000000 2003-01-01 8.05926000000000000 2004-01-01 7.16158999999999950 2005-01-01 6.95541000000000050 2006-01-01 6.63043000000000050 2007-01-01 5.76575000000000000 2008-01-01 4.65651999999999950 2009-01-01 4.70100000000000050 2010-01-01 10.12200000000000000 2011-01-01 10.00070000000000000 2012-01-01 9.27544000000000000 2013-01-01 8.01081999999999900 2014-01-01 9.08363999999999900 2015-01-01 13.48320000000000000 2016-01-01 12.36030000000000000