Year	Percent
1980-01-01	4.915
1981-01-01	4.670
1982-01-01	5.000
1983-01-01	4.500
1984-01-01	4.745
1985-01-01	4.830
1986-01-01	5.000
1987-01-01	5.120
1988-01-01	4.930
1989-01-01	5.420
1990-01-01	5.500
1991-01-01	6.000
1992-01-01	6.805
1993-01-01	6.480
1994-01-01	6.795
1995-01-01	7.030
1996-01-01	7.180
1997-01-01	6.965
1998-01-01	7.625
1999-01-01	7.090
2000-01-01	7.350
2001-01-01	7.085
2002-01-01	7.070
2003-01-01	6.835
2004-01-01	6.420
2005-01-01	6.490
2006-01-01	6.330
2007-01-01	6.410
2008-01-01	6.010
2009-01-01	6.250
2010-01-01	6.140
2011-01-01	6.020
2012-01-01	5.850
2013-01-01	5.920
2014-01-01	5.990
2015-01-01	6.210