Year	Percent
1970-01-01	8.2
1971-01-01	10.0
1972-01-01	9.3
1973-01-01	7.8
1974-01-01	9.1
1975-01-01	13.6
1976-01-01	12.0
1977-01-01	11.0
1978-01-01	9.6
1979-01-01	9.1
1980-01-01	11.5
1981-01-01	12.3
1982-01-01	14.9
1983-01-01	14.5
1984-01-01	11.5
1985-01-01	11.1
1986-01-01	10.7
1987-01-01	9.7
1988-01-01	8.7
1989-01-01	8.6
1990-01-01	8.8
1991-01-01	10.8
1992-01-01	11.4
1993-01-01	10.5
1994-01-01	9.7
1995-01-01	9.1
1996-01-01	9.3
1997-01-01	8.5
1998-01-01	7.9
1999-01-01	7.5
2000-01-01	7.2
2001-01-01	8.3
2002-01-01	9.7
2003-01-01	10.0
2004-01-01	9.4
2005-01-01	8.8
2006-01-01	8.2
2007-01-01	8.2
2008-01-01	10.2
2009-01-01	14.7
2010-01-01	15.5
2011-01-01	14.6
2012-01-01	13.3