Year	Percent
1960-01-01	43.67
1961-01-01	43.20
1962-01-01	42.40
1963-01-01	42.00
1964-01-01	42.02
1965-01-01	41.74
1966-01-01	41.70
1967-01-01	41.47
1968-01-01	41.04
1969-01-01	41.33
1970-01-01	41.51
1971-01-01	41.32
1972-01-01	41.21
1973-01-01	41.45
1974-01-01	41.56
1975-01-01	41.04
1976-01-01	41.21
1977-01-01	41.38
1978-01-01	41.43
1979-01-01	41.50
1980-01-01	41.46
1981-01-01	41.16
1982-01-01	40.99
1983-01-01	40.73
1984-01-01	40.30
1985-01-01	40.00
1986-01-01	40.01
1987-01-01	40.13
1988-01-01	40.28
1989-01-01	40.74
1990-01-01	40.88
1991-01-01	40.73
1992-01-01	40.25
1993-01-01	39.62
1994-01-01	39.64
1995-01-01	39.87
1996-01-01	39.96
1997-01-01	40.09
1998-01-01	40.63
1999-01-01	41.35
2000-01-01	42.14
2001-01-01	42.46
2002-01-01	42.37
2003-01-01	42.13
2004-01-01	41.89
2005-01-01	41.85
2006-01-01	42.01
2007-01-01	42.34
2008-01-01	42.31
2009-01-01	41.54
2010-01-01	41.29
2011-01-01	41.26