Year	Percent
1980-01-01	15.265
1981-01-01	15.020
1982-01-01	14.615
1983-01-01	13.525
1984-01-01	16.705
1985-01-01	17.110
1986-01-01	17.100
1987-01-01	16.065
1988-01-01	21.340
1989-01-01	20.360
1990-01-01	19.870
1991-01-01	21.050
1992-01-01	22.810
1993-01-01	23.810
1994-01-01	14.045
1995-01-01	16.270
1996-01-01	19.370
1997-01-01	18.610
1998-01-01	11.340
1999-01-01	10.390
2000-01-01	11.910
2001-01-01	13.590
2002-01-01	13.160
2003-01-01	14.980
2004-01-01	13.450
2005-01-01	13.940
2006-01-01	9.930
2007-01-01	9.070
2008-01-01	9.670
2009-01-01	13.970
2010-01-01	18.800
2011-01-01	17.050
2012-01-01	17.800
2013-01-01	16.090
2014-01-01	18.990
2015-01-01	18.000