Year	Percent
1966-01-01	0.140
1967-01-01	0.060
1968-01-01	0.075
1969-01-01	0.145
1970-01-01	0.070
1971-01-01	0.210
1972-01-01	0.380
1973-01-01	0.440
1974-01-01	0.430
1975-01-01	0.840
1976-01-01	1.640
1977-01-01	1.525
1978-01-01	1.590
1979-01-01	2.030
1980-01-01	1.875
1981-01-01	2.330
1982-01-01	3.095
1983-01-01	3.930
1984-01-01	5.050
1985-01-01	6.945
1986-01-01	6.555
1987-01-01	7.345
1988-01-01	8.460
1989-01-01	8.805
1990-01-01	7.720
1991-01-01	9.080
1992-01-01	8.770
1993-01-01	11.440
1994-01-01	10.790
1995-01-01	9.740
1996-01-01	10.420
1997-01-01	12.750
1998-01-01	13.780
1999-01-01	17.840
2000-01-01	22.010
2001-01-01	27.380
2002-01-01	31.020
2003-01-01	35.280
2004-01-01	36.290
2005-01-01	34.640
2006-01-01	44.840
2007-01-01	51.830
2008-01-01	49.630
2009-01-01	63.120
2010-01-01	60.620
2011-01-01	61.640
2012-01-01	58.330
2013-01-01	54.730
2014-01-01	53.740
2015-01-01	59.165