Year	Percent
1971-01-01	4.2
1972-01-01	4.4
1973-01-01	3.7
1974-01-01	3.7
1975-01-01	4.5
1976-01-01	5.4
1977-01-01	5.6
1978-01-01	5.5
1979-01-01	5.4
1980-01-01	6.8
1981-01-01	9.7
1982-01-01	10.8
1983-01-01	11.5
1984-01-01	11.8
1985-01-01	11.4
1986-01-01	11.4
1987-01-01	10.5
1988-01-01	8.6
1989-01-01	7.3
1990-01-01	7.1
1991-01-01	8.9
1992-01-01	10.0
1993-01-01	10.4
1994-01-01	9.5
1995-01-01	8.7
1996-01-01	8.1
1997-01-01	7.0
1998-01-01	6.3
1999-01-01	6.0
2000-01-01	5.5
2001-01-01	5.1
2002-01-01	5.2
2003-01-01	5.0
2004-01-01	4.8
2005-01-01	4.9
2006-01-01	5.5
2007-01-01	5.4
2008-01-01	5.7
2009-01-01	7.6
2010-01-01	7.9
2011-01-01	8.1
2012-01-01	8.0