Year	Percent
1980-01-01	1.416
1981-01-01	1.365
1982-01-01	2.195
1983-01-01	2.396
1984-01-01	3.114
1985-01-01	2.760
1986-01-01	3.510
1987-01-01	3.730
1988-01-01	4.140
1989-01-01	4.410
1990-01-01	5.620
1991-01-01	6.690
1992-01-01	7.220
1993-01-01	8.390
1994-01-01	10.280
1995-01-01	9.670
1996-01-01	10.880
1997-01-01	11.610
1998-01-01	12.850
1999-01-01	14.710
2000-01-01	15.720
2001-01-01	17.430
2002-01-01	18.190
2003-01-01	22.410
2004-01-01	20.300
2005-01-01	19.630
2006-01-01	16.440
2007-01-01	17.800
2008-01-01	15.390
2009-01-01	20.900
2010-01-01	19.550
2011-01-01	16.730
2012-01-01	18.630
2013-01-01	17.780
2014-01-01	18.430
2015-01-01	19.100
2016-01-01	22.170