Year	Percent
1984-01-01	22.3
1985-01-01	20.1
1986-01-01	20.3
1987-01-01	17.6
1988-01-01	13.6
1989-01-01	10.6
1990-01-01	12.1
1991-01-01	15.4
1992-01-01	17.0
1993-01-01	19.6
1994-01-01	19.2
1995-01-01	17.6
1996-01-01	18.3
1997-01-01	16.9
1998-01-01	16.7
1999-01-01	16.2
2000-01-01	16.2
2001-01-01	15.6
2002-01-01	16.2
2003-01-01	17.2
2004-01-01	17.4
2005-01-01	18.3
2006-01-01	20.3
2007-01-01	21.4
2008-01-01	21.7
2009-01-01	26.8
2010-01-01	29.1
2011-01-01	31.2
2012-01-01	30.5