Year	Percent
1978-01-01	8.8
1979-01-01	8.8
1980-01-01	8.9
1981-01-01	8.1
1982-01-01	10.4
1983-01-01	14.5
1984-01-01	12.9
1985-01-01	11.5
1986-01-01	11.2
1987-01-01	11.1
1988-01-01	10.4
1989-01-01	8.4
1990-01-01	10.2
1991-01-01	14.3
1992-01-01	16.1
1993-01-01	15.6
1994-01-01	13.6
1995-01-01	12.0
1996-01-01	12.3
1997-01-01	13.2
1998-01-01	11.5
1999-01-01	10.2
2000-01-01	9.1
2001-01-01	10.4
2002-01-01	9.8
2003-01-01	9.2
2004-01-01	8.2
2005-01-01	7.6
2006-01-01	6.7
2007-01-01	6.3
2008-01-01	6.1
2009-01-01	8.2
2010-01-01	8.1
2011-01-01	8.3
2012-01-01	8.6