Year	Percent
1976-01-01	2.28
1977-01-01	2.32
1978-01-01	2.48
1982-01-01	3.01
1984-01-01	1.52
1985-01-01	2.14
1986-01-01	2.64
1987-01-01	2.55
1988-01-01	2.81
1989-01-01	2.87
1990-01-01	2.51
1991-01-01	2.46
1992-01-01	2.56
1993-01-01	2.78
1994-01-01	4.37
1995-01-01	7.24
1996-01-01	4.89
1997-01-01	4.68
1998-01-01	5.46
1999-01-01	6.36
2000-01-01	6.08
2001-01-01	8.10
2002-01-01	9.06
2003-01-01	9.67
2004-01-01	9.86
2005-01-01	10.75
2006-01-01	10.37
2007-01-01	9.43
2008-01-01	8.43
2009-01-01	8.01
2010-01-01	7.25
2011-01-01	6.70
2012-01-01	6.20
2013-01-01	6.03
2014-01-01	5.82
2015-01-01	6.00