Year	Percent
1975-01-01	13.020
1976-01-01	12.620
1977-01-01	12.340
1978-01-01	11.900
1979-01-01	14.570
1980-01-01	9.430
1981-01-01	7.740
1982-01-01	8.285
1983-01-01	10.100
1984-01-01	12.780
1985-01-01	18.245
1986-01-01	25.475
1987-01-01	24.735
1988-01-01	27.330
1989-01-01	25.690
1990-01-01	22.200
1991-01-01	19.140
1992-01-01	17.635
1993-01-01	16.900
1994-01-01	21.640
1995-01-01	21.090
1996-01-01	21.345
1997-01-01	27.510
1998-01-01	29.955
1999-01-01	48.885
2000-01-01	61.280
2001-01-01	55.150
2002-01-01	43.680
2003-01-01	37.920
2004-01-01	42.210
2005-01-01	42.970
2006-01-01	59.950
2007-01-01	60.060
2008-01-01	45.060
2009-01-01	33.960
2010-01-01	32.380
2011-01-01	30.430
2012-01-01	28.470
2013-01-01	38.960
2014-01-01	41.850
2015-01-01	42.540