Year	Percent
1973-01-01	22.530
1974-01-01	22.650
1975-01-01	24.860
1976-01-01	25.510
1977-01-01	26.650
1978-01-01	27.850
1979-01-01	28.300
1980-01-01	29.355
1981-01-01	30.060
1982-01-01	31.910
1983-01-01	34.160
1984-01-01	33.940
1985-01-01	34.460
1986-01-01	35.000
1987-01-01	34.340
1988-01-01	34.375
1989-01-01	34.710
1990-01-01	35.030
1991-01-01	33.290
1992-01-01	32.515
1993-01-01	32.200
1994-01-01	31.450
1995-01-01	30.785
1996-01-01	31.795
1997-01-01	33.490
1998-01-01	33.050
1999-01-01	33.840
2000-01-01	33.330
2001-01-01	35.100
2002-01-01	34.540
2003-01-01	35.580
2004-01-01	36.240
2005-01-01	37.330
2006-01-01	38.045
2007-01-01	41.445
2008-01-01	43.290
2009-01-01	45.770
2010-01-01	46.430
2011-01-01	45.110
2012-01-01	47.585
2013-01-01	47.980
2014-01-01	49.560
2015-01-01	55.090