Year Percent 1980-01-01 1.465510000000000 1981-01-01 1.346600000000000 1982-01-01 3.401270000000000 1983-01-01 6.741460000000001 1984-01-01 8.802410000000000 1985-01-01 16.007700000000000 1986-01-01 19.430200000000000 1987-01-01 19.278200000000000 1988-01-01 16.581200000000000 1989-01-01 14.602300000000000 1990-01-01 13.511900000000000 1991-01-01 12.430500000000000 1992-01-01 8.272610000000000 1993-01-01 6.688780000000000 1994-01-01 6.376890000000000 1995-01-01 6.879770000000000 1996-01-01 8.381200000000000 1997-01-01 11.439000000000000 1998-01-01 15.287700000000000 1999-01-01 16.997000000000000 2000-01-01 15.498800000000000 2001-01-01 17.129500000000000 2002-01-01 20.981600000000000 2003-01-01 19.361900000000000 2004-01-01 20.922800000000000 2005-01-01 18.919600000000000 2006-01-01 18.531400000000000 2007-01-01 15.705900000000000 2008-01-01 13.523100000000000 2009-01-01 15.748700000000000 2010-01-01 15.471100000000000 2011-01-01 13.698900000000000 2012-01-01 15.971700000000000 2013-01-01 16.410000000000000 2014-01-01 16.126200000000000 2015-01-01 19.904000000000000 2016-01-01 21.213400000000000