Year	Percent
1978-01-01	48.2597579021027
1979-01-01	48.6233051595135
1980-01-01	48.7020247739952
1981-01-01	48.7340467838999
1982-01-01	49.1161379385801
1983-01-01	50.0493058386437
1984-01-01	49.9541359638663
1985-01-01	49.9658244592951
1986-01-01	49.9228674396885
1987-01-01	50.0887792763388
1988-01-01	50.5563407364737
1989-01-01	51.4572975140805
1990-01-01	52.2769911303579
1991-01-01	52.9832475605138
1992-01-01	53.1906537955584
1993-01-01	52.6729963247409
1994-01-01	52.4709937391555
1995-01-01	52.2716231136102
1996-01-01	52.4172934484736
1997-01-01	52.9114517555831
1998-01-01	52.5340494374063
1999-01-01	51.9342080750206
2000-01-01	51.8015091228701
2001-01-01	51.7941936276654
2002-01-01	51.1990548032029
2003-01-01	51.2858134633604
2004-01-01	51.7617195574175
2005-01-01	52.2880569516682
2006-01-01	52.8714978183643
2007-01-01	53.2641877505650
2008-01-01	53.4259599231123
2009-01-01	53.3604540287708
2010-01-01	53.7056325225510
2011-01-01	53.9197268384124
2012-01-01	54.2054905762766
2013-01-01	55.5675386899205
2014-01-01	56.3979603746478
2015-01-01	57.1702469606648
2016-01-01	58.4546824433947
2017-01-01	59.7886639189512