Year	Percent
1970-01-01	47.4
1971-01-01	47.1
1972-01-01	45.9
1973-01-01	45.8
1974-01-01	46.2
1975-01-01	46.0
1976-01-01	46.1
1977-01-01	46.2
1978-01-01	45.9
1979-01-01	45.9
1980-01-01	46.0
1981-01-01	45.9
1982-01-01	45.1
1983-01-01	44.7
1984-01-01	44.5
1985-01-01	44.4
1986-01-01	44.2
1987-01-01	43.8
1988-01-01	43.7
1989-01-01	43.6
1990-01-01	43.9
1991-01-01	44.5
1992-01-01	44.0
1993-01-01	44.5
1994-01-01	43.6
1995-01-01	43.1
1996-01-01	43.2
1997-01-01	43.2
1998-01-01	43.5
1999-01-01	43.9
2000-01-01	44.5
2001-01-01	45.1
2002-01-01	45.6
2003-01-01	45.3
2004-01-01	45.1
2005-01-01	44.9
2006-01-01	45.5
2007-01-01	45.6
2008-01-01	45.6
2009-01-01	44.6
2010-01-01	44.0
2011-01-01	44.0
2012-01-01	43.7