Year	Percent
1980-01-01	0.640
1981-01-01	0.650
1982-01-01	0.800
1983-01-01	0.905
1984-01-01	0.995
1985-01-01	1.470
1986-01-01	1.530
1987-01-01	1.525
1988-01-01	1.430
1989-01-01	1.140
1990-01-01	2.010
1991-01-01	1.540
1992-01-01	1.610
1993-01-01	2.670
1994-01-01	3.520
1995-01-01	3.540
1996-01-01	3.185
1997-01-01	3.150
1998-01-01	3.745
1999-01-01	4.520
2000-01-01	5.250
2001-01-01	5.330
2002-01-01	5.710
2003-01-01	5.250
2004-01-01	5.520
2005-01-01	4.140
2006-01-01	3.880
2007-01-01	3.750
2008-01-01	3.575
2009-01-01	4.740
2010-01-01	5.370
2011-01-01	5.030
2012-01-01	5.440
2013-01-01	5.410
2014-01-01	5.840
2015-01-01	6.455