Year	Percent
1973-01-01	2.6
1974-01-01	2.8
1975-01-01	3.9
1976-01-01	4.1
1977-01-01	3.8
1978-01-01	3.6
1979-01-01	3.6
1980-01-01	4.2
1981-01-01	6.9
1982-01-01	8.6
1983-01-01	10.4
1984-01-01	10.4
1985-01-01	8.4
1986-01-01	7.9
1987-01-01	7.3
1988-01-01	7.3
1989-01-01	6.5
1990-01-01	5.6
1991-01-01	5.4
1992-01-01	5.4
1993-01-01	5.3
1994-01-01	6.1
1995-01-01	5.9
1996-01-01	5.3
1997-01-01	4.5
1998-01-01	3.5
1999-01-01	2.8
2000-01-01	2.4
2001-01-01	2.0
2002-01-01	2.7
2003-01-01	4.0
2004-01-01	4.8
2005-01-01	4.9
2006-01-01	3.8
2007-01-01	3.1
2008-01-01	2.8
2009-01-01	3.7
2010-01-01	4.4
2011-01-01	4.5
2012-01-01	5.4