Year	Percent
1978-01-01	4.0
1979-01-01	3.8
1980-01-01	3.7
1981-01-01	3.7
1982-01-01	4.7
1983-01-01	7.0
1984-01-01	6.3
1985-01-01	5.9
1986-01-01	5.7
1987-01-01	5.9
1988-01-01	5.3
1989-01-01	4.6
1990-01-01	5.1
1991-01-01	7.3
1992-01-01	8.4
1993-01-01	8.7
1994-01-01	7.7
1995-01-01	6.6
1996-01-01	6.7
1997-01-01	6.5
1998-01-01	6.0
1999-01-01	5.4
2000-01-01	4.9
2001-01-01	5.1
2002-01-01	4.9
2003-01-01	4.5
2004-01-01	4.0
2005-01-01	3.7
2006-01-01	3.6
2007-01-01	3.2
2008-01-01	3.2
2009-01-01	4.3
2010-01-01	3.8
2011-01-01	3.7
2012-01-01	3.9