Year	Percent
1978-01-01	24.2815
1979-01-01	22.3304
1980-01-01	24.4066
1981-01-01	20.0164
1982-01-01	17.6296
1983-01-01	18.2968
1984-01-01	21.5529
1985-01-01	23.7568
1986-01-01	24.3979
1987-01-01	23.7007
1988-01-01	28.3864
1989-01-01	31.6089
1990-01-01	24.3871
1991-01-01	26.0799
1992-01-01	25.1512
1993-01-01	25.2536
1994-01-01	23.9569
1995-01-01	22.6197
1996-01-01	21.1625
1997-01-01	20.0214
1998-01-01	20.6978
1999-01-01	21.8076
2000-01-01	25.4297
2001-01-01	22.3374
2002-01-01	18.2723
2003-01-01	18.8906
2004-01-01	19.3897
2005-01-01	20.0751
2006-01-01	23.7095
2007-01-01	26.3356
2008-01-01	26.1814
2009-01-01	24.3963
2010-01-01	22.0297
2011-01-01	21.0555
2012-01-01	22.9491
2013-01-01	26.4541
2014-01-01	28.8993
2015-01-01	28.2696
2016-01-01	29.5552