Year	Percent
1976-01-01	12.4
1977-01-01	13.8
1978-01-01	13.9
1979-01-01	12.6
1980-01-01	12.7
1981-01-01	12.6
1982-01-01	18.1
1983-01-01	19.1
1984-01-01	17.2
1985-01-01	15.6
1986-01-01	14.5
1987-01-01	13.0
1988-01-01	11.2
1989-01-01	10.5
1990-01-01	12.0
1991-01-01	15.4
1992-01-01	16.8
1993-01-01	16.7
1994-01-01	14.9
1995-01-01	13.9
1996-01-01	14.5
1997-01-01	15.5
1998-01-01	14.6
1999-01-01	13.4
2000-01-01	11.7
2001-01-01	11.9
2002-01-01	12.9
2003-01-01	12.8
2004-01-01	12.5
2005-01-01	11.4
2006-01-01	10.6
2007-01-01	10.0
2008-01-01	10.4
2009-01-01	13.9
2010-01-01	13.6
2011-01-01	12.8
2012-01-01	13.0