Year	Percent
1972-01-01	1.7
1973-01-01	1.6
1974-01-01	1.5
1975-01-01	2.3
1976-01-01	1.8
1977-01-01	1.5
1978-01-01	1.8
1979-01-01	2.0
1980-01-01	1.7
1981-01-01	2.0
1982-01-01	2.6
1983-01-01	3.4
1984-01-01	3.2
1985-01-01	2.6
1986-01-01	2.0
1987-01-01	2.1
1988-01-01	3.2
1989-01-01	5.4
1990-01-01	5.8
1991-01-01	6.0
1992-01-01	6.5
1993-01-01	6.6
1994-01-01	6.0
1995-01-01	5.5
1996-01-01	4.8
1997-01-01	3.9
1998-01-01	3.1
1999-01-01	3.0
2000-01-01	3.2
2001-01-01	3.4
2002-01-01	3.7
2003-01-01	4.2
2004-01-01	4.3
2005-01-01	4.5
2006-01-01	3.4
2007-01-01	2.5
2008-01-01	2.5
2009-01-01	3.2
2010-01-01	3.6
2011-01-01	3.3