Year	Percent
1970-01-01	33.6
1971-01-01	34.4
1972-01-01	34.9
1973-01-01	35.6
1974-01-01	36.1
1975-01-01	36.9
1976-01-01	37.4
1977-01-01	37.9
1978-01-01	38.6
1979-01-01	39.2
1980-01-01	39.8
1981-01-01	40.5
1982-01-01	40.9
1983-01-01	41.4
1984-01-01	41.9
1985-01-01	42.4
1986-01-01	42.7
1987-01-01	43.1
1988-01-01	43.6
1989-01-01	43.9
1990-01-01	44.2
1991-01-01	44.6
1992-01-01	44.7
1993-01-01	44.9
1994-01-01	44.9
1995-01-01	45.1
1996-01-01	45.2
1997-01-01	45.3
1998-01-01	45.5
1999-01-01	45.7
2000-01-01	45.9
2001-01-01	46.0
2002-01-01	46.2
2003-01-01	46.5
2004-01-01	46.6
2005-01-01	46.5
2006-01-01	46.8
2007-01-01	47.0
2008-01-01	47.0
2009-01-01	47.2
2010-01-01	47.2
2011-01-01	47.2
2012-01-01	47.3