Year	Percent
1971-01-01	5.1
1972-01-01	5.1
1973-01-01	4.8
1974-01-01	4.7
1975-01-01	5.2
1976-01-01	5.9
1977-01-01	6.2
1978-01-01	6.2
1979-01-01	6.2
1980-01-01	7.1
1981-01-01	8.8
1982-01-01	9.5
1983-01-01	10.5
1984-01-01	11.6
1985-01-01	11.0
1986-01-01	10.9
1987-01-01	10.0
1988-01-01	8.3
1989-01-01	7.1
1990-01-01	6.8
1991-01-01	7.5
1992-01-01	7.7
1993-01-01	7.9
1994-01-01	7.4
1995-01-01	6.9
1996-01-01	6.4
1997-01-01	5.9
1998-01-01	5.4
1999-01-01	5.2
2000-01-01	4.9
2001-01-01	4.5
2002-01-01	4.5
2003-01-01	4.4
2004-01-01	4.3
2005-01-01	4.4
2006-01-01	5.0
2007-01-01	5.0
2008-01-01	5.1
2009-01-01	6.4
2010-01-01	6.9
2011-01-01	7.3
2012-01-01	7.4