Year	Percent
1960-01-01	42.71
1961-01-01	42.95
1962-01-01	42.84
1963-01-01	42.69
1964-01-01	42.49
1965-01-01	42.54
1966-01-01	42.36
1967-01-01	42.25
1968-01-01	41.93
1969-01-01	41.95
1970-01-01	42.33
1971-01-01	42.40
1972-01-01	42.57
1973-01-01	42.57
1974-01-01	42.87
1975-01-01	43.34
1976-01-01	44.58
1977-01-01	45.62
1978-01-01	46.24
1979-01-01	46.72
1980-01-01	47.70
1981-01-01	48.15
1982-01-01	47.99
1983-01-01	47.73
1984-01-01	47.95
1985-01-01	49.14
1986-01-01	50.56
1987-01-01	51.35
1988-01-01	50.80
1989-01-01	49.15
1990-01-01	48.54
1991-01-01	47.83
1992-01-01	47.46
1993-01-01	47.51
1994-01-01	47.88
1995-01-01	48.63
1996-01-01	49.36
1997-01-01	50.53
1998-01-01	51.57
1999-01-01	51.69
2000-01-01	51.65
2001-01-01	51.57
2002-01-01	51.49
2003-01-01	50.59
2004-01-01	50.53
2005-01-01	50.83
2006-01-01	52.17
2007-01-01	53.76
2008-01-01	54.81
2009-01-01	53.88
2010-01-01	53.17
2011-01-01	53.22