Year	Percent
1976-01-01	42.42
1977-01-01	43.58
1978-01-01	45.70
1979-01-01	48.09
1980-01-01	50.09
1981-01-01	49.31
1982-01-01	48.38
1983-01-01	48.89
1984-01-01	48.27
1985-01-01	46.89
1986-01-01	46.17
1987-01-01	47.44
1988-01-01	48.62
1989-01-01	49.42
1990-01-01	52.42
1991-01-01	50.52
1992-01-01	50.70
1993-01-01	49.93
1994-01-01	50.13
1995-01-01	50.18
1996-01-01	51.07
1997-01-01	52.32
1998-01-01	51.80
1999-01-01	51.60
2000-01-01	52.55
2001-01-01	52.47
2002-01-01	51.71
2003-01-01	52.05
2004-01-01	52.10
2005-01-01	53.06
2006-01-01	54.71
2007-01-01	56.95
2008-01-01	58.72
2009-01-01	59.57
2010-01-01	60.04
2011-01-01	61.10