Year	Percent
1975-01-01	8.000
1976-01-01	11.690
1977-01-01	7.165
1978-01-01	13.290
1979-01-01	16.665
1980-01-01	16.840
1981-01-01	20.130
1982-01-01	13.420
1983-01-01	22.690
1984-01-01	20.395
1985-01-01	26.260
1986-01-01	24.100
1987-01-01	42.300
1988-01-01	26.845
1989-01-01	23.395
1990-01-01	24.560
1991-01-01	21.070
1992-01-01	21.720
1993-01-01	24.880
1994-01-01	23.940
1995-01-01	18.185
1996-01-01	19.810
1997-01-01	30.005
1998-01-01	30.465
1999-01-01	28.820
2000-01-01	24.770
2001-01-01	17.745
2002-01-01	16.790
2003-01-01	12.880
2004-01-01	17.120
2005-01-01	16.380
2006-01-01	18.230
2007-01-01	28.355
2008-01-01	18.100
2009-01-01	20.840
2010-01-01	15.140
2011-01-01	11.740
2012-01-01	10.125
2013-01-01	26.950
2014-01-01	29.365
2015-01-01	28.760