Year	Percent
1973-01-01	2.8
1974-01-01	3.1
1975-01-01	4.1
1976-01-01	4.2
1977-01-01	3.8
1978-01-01	3.7
1979-01-01	3.7
1980-01-01	4.3
1981-01-01	6.4
1982-01-01	7.4
1983-01-01	8.8
1984-01-01	8.9
1985-01-01	7.6
1986-01-01	8.2
1987-01-01	8.2
1988-01-01	8.0
1989-01-01	7.3
1990-01-01	6.6
1991-01-01	6.2
1992-01-01	6.1
1993-01-01	5.4
1994-01-01	6.2
1995-01-01	5.9
1996-01-01	5.4
1997-01-01	4.8
1998-01-01	3.6
1999-01-01	2.8
2000-01-01	2.5
2001-01-01	2.0
2002-01-01	2.5
2003-01-01	3.5
2004-01-01	4.3
2005-01-01	4.5
2006-01-01	3.7
2007-01-01	2.9
2008-01-01	2.4
2009-01-01	2.9
2010-01-01	3.7
2011-01-01	3.9
2012-01-01	4.5