Year	Percent
1980-01-01	7.29
1981-01-01	7.69
1982-01-01	7.90
1983-01-01	8.46
1984-01-01	8.62
1985-01-01	8.86
1986-01-01	9.91
1987-01-01	11.00
1988-01-01	11.47
1989-01-01	11.63
1990-01-01	11.96
1991-01-01	12.52
1992-01-01	23.57
1993-01-01	25.82
1994-01-01	25.76
1995-01-01	27.38
1996-01-01	30.94
1997-01-01	35.16
1998-01-01	41.43
1999-01-01	43.20
2000-01-01	43.21
2001-01-01	44.83
2002-01-01	45.04
2003-01-01	49.88
2004-01-01	56.01
2005-01-01	60.83
2006-01-01	63.19
2007-01-01	64.00
2008-01-01	60.92
2009-01-01	67.55
2010-01-01	68.06
2011-01-01	67.46
2012-01-01	68.22
2013-01-01	68.99
2014-01-01	70.06
2015-01-01	69.53