Year Percent 1980-01-01 0.0020780000000000000 1981-01-01 0.0022960000000000003 1982-01-01 0.2713530000000000000 1983-01-01 0.3419120000000000000 1984-01-01 0.6499790000000000000 1985-01-01 1.1098800000000000000 1986-01-01 0.9432320000000000000 1987-01-01 1.3069000000000000000 1988-01-01 1.2513100000000001000 1989-01-01 1.1142200000000000000 1990-01-01 1.2499600000000000000 1991-01-01 1.5992600000000001000 1992-01-01 1.3389600000000000000 1993-01-01 2.7252600000000000000 1994-01-01 3.6934400000000003000 1995-01-01 4.1243700000000000000 1996-01-01 3.9335100000000000000 1997-01-01 4.2115700000000000000 1998-01-01 4.6847699999999990000 1999-01-01 4.4389100000000000000 2000-01-01 5.7907100000000000000 2001-01-01 6.2143900000000000000 2002-01-01 6.9755600000000010000 2003-01-01 7.6366200000000000000 2004-01-01 8.0707300000000010000 2005-01-01 7.4299000000000000000 2006-01-01 7.3405200000000000000 2007-01-01 6.8865300000000005000 2008-01-01 5.2115000000000000000 2009-01-01 5.9754100000000000000 2010-01-01 6.8353100000000010000 2011-01-01 6.1903100000000000000 2012-01-01 6.6579399999999990000 2013-01-01 6.4733500000000000000 2014-01-01 5.4623500000000000000 2015-01-01 5.2558400000000000000 2016-01-01 4.9295500000000000000