Year	Percent
1970-01-01	5.2
1971-01-01	5.2
1972-01-01	6.0
1973-01-01	6.2
1974-01-01	5.2
1975-01-01	5.7
1976-01-01	6.7
1977-01-01	6.8
1978-01-01	6.9
1979-01-01	7.4
1980-01-01	7.4
1981-01-01	8.1
1982-01-01	8.7
1983-01-01	9.4
1984-01-01	9.3
1985-01-01	9.4
1986-01-01	11.8
1987-01-01	12.2
1988-01-01	12.3
1989-01-01	12.1
1990-01-01	10.8
1991-01-01	10.4
1992-01-01	10.8
1993-01-01	14.0
1994-01-01	14.7
1995-01-01	15.5
1996-01-01	15.3
1997-01-01	15.4
1998-01-01	15.5
1999-01-01	14.8
2000-01-01	13.6
2001-01-01	12.1
2002-01-01	11.4
2003-01-01	11.4
2004-01-01	10.6
2005-01-01	10.1
2006-01-01	8.8
2007-01-01	7.9
2008-01-01	8.5
2009-01-01	9.3
2010-01-01	9.7
2011-01-01	9.6
2012-01-01	11.9