Year	Percent
1973-01-01	51.8
1974-01-01	51.6
1975-01-01	51.7
1976-01-01	51.2
1977-01-01	51.6
1978-01-01	51.3
1979-01-01	51.4
1980-01-01	52.1
1981-01-01	51.7
1982-01-01	50.8
1983-01-01	49.3
1984-01-01	49.3
1985-01-01	50.1
1986-01-01	50.3
1987-01-01	49.8
1988-01-01	50.7
1989-01-01	51.4
1990-01-01	52.7
1991-01-01	53.6
1992-01-01	54.3
1993-01-01	53.9
1994-01-01	54.0
1995-01-01	55.3
1996-01-01	56.2
1997-01-01	57.7
1998-01-01	59.0
1999-01-01	60.2
2000-01-01	61.4
2001-01-01	62.5
2002-01-01	62.8
2003-01-01	62.2
2004-01-01	61.8
2005-01-01	61.5
2006-01-01	62.4
2007-01-01	63.6
2008-01-01	64.2
2009-01-01	63.8
2010-01-01	61.7
2011-01-01	61.3
2012-01-01	61.4