Year	Percent
1960-01-01	3.200
1961-01-01	3.560
1962-01-01	3.130
1963-01-01	3.395
1964-01-01	2.660
1965-01-01	2.550
1966-01-01	2.880
1967-01-01	2.460
1968-01-01	2.445
1969-01-01	2.765
1970-01-01	2.190
1971-01-01	2.640
1972-01-01	2.105
1973-01-01	1.655
1974-01-01	1.570
1975-01-01	2.000
1976-01-01	2.140
1977-01-01	2.000
1978-01-01	2.070
1979-01-01	2.420
1980-01-01	3.450
1981-01-01	3.080
1982-01-01	3.000
1983-01-01	2.950
1984-01-01	2.830
1985-01-01	2.355
1986-01-01	2.030
1987-01-01	1.870
1988-01-01	1.735
1989-01-01	1.640
1990-01-01	1.695
1991-01-01	1.600
1992-01-01	1.220
1993-01-01	1.135
1994-01-01	1.070
1995-01-01	0.900
1996-01-01	0.880
1997-01-01	0.890
1998-01-01	0.830
1999-01-01	0.540
2000-01-01	0.405
2001-01-01	0.335
2002-01-01	0.255
2003-01-01	0.285
2004-01-01	0.330
2005-01-01	0.290
2006-01-01	0.240
2007-01-01	0.200
2008-01-01	0.220
2009-01-01	0.555
2010-01-01	0.620
2011-01-01	0.860
2012-01-01	0.975
2013-01-01	0.985
2014-01-01	1.090
2015-01-01	2.880