Year	Percent
1987-01-01	21.0
1988-01-01	18.6
1989-01-01	17.5
1990-01-01	15.5
1991-01-01	15.7
1992-01-01	12.0
1993-01-01	12.1
1994-01-01	12.4
1995-01-01	18.6
1996-01-01	17.9
1997-01-01	14.8
1998-01-01	12.1
1999-01-01	11.0
2000-01-01	8.9
2001-01-01	6.9
2002-01-01	7.8
2003-01-01	9.6
2004-01-01	10.8
2005-01-01	11.5
2006-01-01	9.9
2007-01-01	9.8
2008-01-01	8.2
2009-01-01	9.4
2010-01-01	11.2
2011-01-01	10.5
2012-01-01	12.8