Year	Percent
1987-01-01	12.3
1988-01-01	11.8
1989-01-01	10.1
1990-01-01	9.6
1991-01-01	8.5
1992-01-01	8.7
1993-01-01	9.0
1994-01-01	9.5
1995-01-01	10.1
1996-01-01	8.9
1997-01-01	6.3
1998-01-01	5.6
1999-01-01	4.3
2000-01-01	3.8
2001-01-01	3.6
2002-01-01	3.7
2003-01-01	5.1
2004-01-01	6.9
2005-01-01	7.2
2006-01-01	5.1
2007-01-01	4.4
2008-01-01	4.4
2009-01-01	6.1
2010-01-01	7.0
2011-01-01	5.7
2012-01-01	7.2