Year	Percent
1960-01-01	41.68
1961-01-01	41.67
1962-01-01	41.27
1963-01-01	40.29
1964-01-01	39.82
1965-01-01	38.52
1966-01-01	37.60
1967-01-01	37.79
1968-01-01	37.54
1969-01-01	37.06
1970-01-01	37.03
1971-01-01	36.87
1972-01-01	36.57
1973-01-01	36.83
1974-01-01	37.16
1975-01-01	36.97
1976-01-01	37.16
1977-01-01	37.11
1978-01-01	37.11
1979-01-01	37.41
1980-01-01	37.87
1981-01-01	37.80
1982-01-01	37.85
1983-01-01	37.95
1984-01-01	37.94
1985-01-01	38.29
1986-01-01	38.55
1987-01-01	38.64
1988-01-01	39.03
1989-01-01	39.27
1990-01-01	39.86
1991-01-01	40.57
1992-01-01	40.26
1993-01-01	39.15
1994-01-01	38.50
1995-01-01	38.42
1996-01-01	38.63
1997-01-01	38.73
1998-01-01	39.10
1999-01-01	39.52
2000-01-01	40.27
2001-01-01	41.06
2002-01-01	41.63
2003-01-01	41.92
2004-01-01	41.69
2005-01-01	41.63
2006-01-01	42.20
2007-01-01	42.42
2008-01-01	42.21
2009-01-01	41.27
2010-01-01	40.77
2011-01-01	40.73