Year Percent 1980-01-01 0.58914000000000000 1981-01-01 0.62579200000000000 1982-01-01 0.66743500000000000 1983-01-01 0.84069599999999990 1984-01-01 0.82451600000000000 1985-01-01 0.82938200000000000 1986-01-01 0.26685400000000000 1987-01-01 0.22333100000000000 1988-01-01 0.19645200000000000 1989-01-01 0.16133900000000000 1990-01-01 0.16133900000000000 1991-01-01 0.16133900000000000 1992-01-01 0.12190699999999999 1993-01-01 1.15967999999999980 1994-01-01 0.84051300000000000 1995-01-01 0.55399300000000010 1996-01-01 2.21245999999999960 1997-01-01 3.21377000000000020 1998-01-01 4.15383000000000000 1999-01-01 5.68730000000000000 2000-01-01 6.06890000000000000 2001-01-01 8.14586000000000000 2002-01-01 9.71010000000000000 2003-01-01 8.91628000000000000 2004-01-01 6.78715000000000000 2005-01-01 5.81061000000000000 2006-01-01 4.70624000000000000 2007-01-01 4.13930000000000000 2008-01-01 4.22479000000000050 2009-01-01 5.51136999999999900 2010-01-01 5.67325000000000000 2011-01-01 6.05188000000000100 2012-01-01 7.61274000000000000 2013-01-01 11.05020000000000000 2014-01-01 14.94390000000000000 2015-01-01 18.33300000000000000 2016-01-01 18.49480000000000000