Year	Percent
1960-01-01	45.58
1961-01-01	45.73
1962-01-01	45.56
1963-01-01	45.39
1964-01-01	45.69
1965-01-01	45.85
1966-01-01	45.71
1967-01-01	44.92
1968-01-01	44.51
1969-01-01	44.33
1970-01-01	44.08
1971-01-01	43.82
1972-01-01	43.82
1973-01-01	44.40
1974-01-01	44.51
1975-01-01	44.34
1976-01-01	44.09
1977-01-01	44.15
1978-01-01	44.39
1979-01-01	44.80
1980-01-01	44.53
1981-01-01	43.35
1982-01-01	42.55
1983-01-01	42.22
1984-01-01	43.05
1985-01-01	43.48
1986-01-01	43.66
1987-01-01	44.43
1988-01-01	45.80
1989-01-01	46.87
1990-01-01	46.95
1991-01-01	45.55
1992-01-01	44.35
1993-01-01	43.84
1994-01-01	44.08
1995-01-01	44.49
1996-01-01	44.80
1997-01-01	45.49
1998-01-01	45.82
1999-01-01	46.30
2000-01-01	46.67
2001-01-01	46.88
2002-01-01	47.07
2003-01-01	47.32
2004-01-01	47.59
2005-01-01	47.76
2006-01-01	47.91
2007-01-01	47.93
2008-01-01	47.95
2009-01-01	46.87
2010-01-01	46.69
2011-01-01	46.57