Year	Percent
1978-01-01	12.6
1979-01-01	13.0
1980-01-01	12.5
1981-01-01	11.4
1982-01-01	13.8
1983-01-01	18.3
1984-01-01	16.8
1985-01-01	15.2
1986-01-01	15.0
1987-01-01	14.9
1988-01-01	13.4
1989-01-01	11.2
1990-01-01	13.0
1991-01-01	17.5
1992-01-01	19.4
1993-01-01	18.7
1994-01-01	17.1
1995-01-01	15.4
1996-01-01	15.7
1997-01-01	16.1
1998-01-01	14.6
1999-01-01	13.3
2000-01-01	12.1
2001-01-01	13.5
2002-01-01	12.8
2003-01-01	12.0
2004-01-01	11.4
2005-01-01	10.6
2006-01-01	10.0
2007-01-01	9.4
2008-01-01	8.8
2009-01-01	11.5
2010-01-01	11.6
2011-01-01	11.4
2012-01-01	11.7