Year	Percent
1981-01-01	2.01
1982-01-01	2.44
1983-01-01	0.52
1984-01-01	0.54
1985-01-01	0.72
1986-01-01	1.16
1987-01-01	1.36
1988-01-01	1.46
1989-01-01	1.23
1990-01-01	1.46
1991-01-01	2.40
1992-01-01	5.04
1993-01-01	1.80
1994-01-01	2.21
1995-01-01	3.55
1996-01-01	5.17
1997-01-01	6.23
1998-01-01	6.45
1999-01-01	3.94
2000-01-01	6.12
2001-01-01	7.10
2002-01-01	9.44
2003-01-01	9.60
2004-01-01	11.00
2005-01-01	10.22
2006-01-01	11.69
2007-01-01	13.46
2008-01-01	12.16
2009-01-01	18.23
2010-01-01	16.25
2011-01-01	14.11
2012-01-01	13.86
2013-01-01	14.12
2014-01-01	17.95
2015-01-01	17.84
2016-01-01	18.46