Year	Percent
1975-01-01	15.435
1976-01-01	15.130
1977-01-01	13.805
1978-01-01	11.360
1979-01-01	14.885
1980-01-01	12.100
1981-01-01	14.080
1982-01-01	14.660
1983-01-01	20.430
1984-01-01	25.765
1985-01-01	33.010
1986-01-01	36.570
1987-01-01	38.740
1988-01-01	38.110
1989-01-01	21.550
1990-01-01	19.725
1991-01-01	17.935
1992-01-01	17.005
1993-01-01	15.915
1994-01-01	22.020
1995-01-01	18.460
1996-01-01	17.750
1997-01-01	19.740
1998-01-01	19.570
1999-01-01	23.140
2000-01-01	28.125
2001-01-01	21.630
2002-01-01	22.125
2003-01-01	23.080
2004-01-01	26.990
2005-01-01	33.715
2006-01-01	36.790
2007-01-01	51.570
2008-01-01	40.830
2009-01-01	33.730
2010-01-01	35.110
2011-01-01	30.430
2012-01-01	30.440
2013-01-01	45.735
2014-01-01	47.425
2015-01-01	55.235