Year	Percent
1980-01-01	17.040
1981-01-01	16.300
1982-01-01	17.750
1983-01-01	18.160
1984-01-01	18.350
1985-01-01	19.660
1986-01-01	21.030
1987-01-01	21.190
1988-01-01	21.995
1989-01-01	22.260
1990-01-01	14.790
1991-01-01	20.245
1992-01-01	21.385
1993-01-01	23.155
1994-01-01	23.480
1995-01-01	25.200
1996-01-01	25.890
1997-01-01	18.730
1998-01-01	9.180
1999-01-01	19.280
2000-01-01	8.550
2001-01-01	5.080
2002-01-01	5.710
2003-01-01	4.785
2004-01-01	4.760
2005-01-01	4.345
2006-01-01	3.780
2007-01-01	3.710
2008-01-01	3.730
2009-01-01	3.950
2010-01-01	4.045
2011-01-01	4.075
2012-01-01	4.380
2013-01-01	4.690
2014-01-01	7.110
2015-01-01	6.780