Year	Percent
1970-01-01	0.350
1971-01-01	0.460
1972-01-01	0.490
1973-01-01	0.520
1974-01-01	0.400
1975-01-01	0.525
1976-01-01	0.775
1977-01-01	0.875
1978-01-01	0.945
1979-01-01	0.890
1980-01-01	0.865
1981-01-01	0.860
1982-01-01	0.820
1983-01-01	0.780
1984-01-01	0.730
1985-01-01	0.700
1986-01-01	0.630
1987-01-01	0.530
1988-01-01	0.510
1989-01-01	0.500
1990-01-01	0.430
1991-01-01	0.450
1992-01-01	0.420
1993-01-01	0.425
1994-01-01	0.460
1995-01-01	0.455
1996-01-01	0.480
1997-01-01	0.450
1998-01-01	0.530
1999-01-01	0.620
2000-01-01	0.410
2001-01-01	0.380
2002-01-01	0.340
2003-01-01	0.520
2004-01-01	0.630
2005-01-01	0.640
2006-01-01	0.670
2007-01-01	0.670
2008-01-01	0.750
2009-01-01	0.730
2010-01-01	0.750
2011-01-01	0.800
2012-01-01	0.850
2013-01-01	0.870
2014-01-01	0.890
2015-01-01	0.970