Year	Percent
1973-01-01	28.5
1974-01-01	28.7
1975-01-01	29.5
1976-01-01	29.9
1977-01-01	30.6
1978-01-01	31.1
1979-01-01	32.1
1980-01-01	34.3
1981-01-01	36.7
1982-01-01	37.9
1983-01-01	37.1
1984-01-01	38.0
1985-01-01	37.9
1986-01-01	40.2
1987-01-01	41.0
1988-01-01	42.3
1989-01-01	42.6
1990-01-01	44.2
1991-01-01	45.2
1992-01-01	46.0
1993-01-01	46.2
1994-01-01	47.0
1995-01-01	48.6
1996-01-01	49.4
1997-01-01	50.8
1998-01-01	51.4
1999-01-01	52.7
2000-01-01	53.9
2001-01-01	55.0
2002-01-01	56.0
2003-01-01	56.3
2004-01-01	56.7
2005-01-01	57.3
2006-01-01	57.8
2007-01-01	59.0
2008-01-01	59.5
2009-01-01	59.8
2010-01-01	58.4
2011-01-01	58.3
2012-01-01	58.9