Year	Percent
1971-01-01	60.2
1972-01-01	60.1
1973-01-01	60.8
1974-01-01	60.7
1975-01-01	60.2
1976-01-01	59.6
1977-01-01	59.2
1978-01-01	59.1
1979-01-01	59.3
1980-01-01	58.5
1981-01-01	56.6
1982-01-01	55.2
1983-01-01	54.5
1984-01-01	55.3
1985-01-01	55.7
1986-01-01	55.8
1987-01-01	56.6
1988-01-01	58.3
1989-01-01	59.6
1990-01-01	59.8
1991-01-01	58.1
1992-01-01	56.6
1993-01-01	56.1
1994-01-01	56.4
1995-01-01	57.0
1996-01-01	57.3
1997-01-01	58.1
1998-01-01	58.5
1999-01-01	59.0
2000-01-01	59.4
2001-01-01	59.5
2002-01-01	59.6
2003-01-01	59.8
2004-01-01	59.9
2005-01-01	60.0
2006-01-01	60.0
2007-01-01	60.0
2008-01-01	59.9
2009-01-01	58.5
2010-01-01	58.2
2011-01-01	58.0
2012-01-01	58.3