Year	Percent
1980-01-01	17.06
1981-01-01	16.30
1982-01-01	17.75
1983-01-01	18.16
1984-01-01	18.35
1985-01-01	19.66
1986-01-01	21.03
1987-01-01	21.19
1988-01-01	21.27
1989-01-01	22.26
1990-01-01	20.74
1991-01-01	22.88
1992-01-01	24.02
1993-01-01	25.29
1994-01-01	23.48
1995-01-01	25.20
1996-01-01	25.89
1997-01-01	25.85
1998-01-01	25.56
1999-01-01	24.30
2000-01-01	23.98
2001-01-01	24.18
2002-01-01	24.57
2003-01-01	26.07
2004-01-01	26.24
2005-01-01	25.59
2006-01-01	26.07
2007-01-01	25.07
2008-01-01	23.20
2009-01-01	43.97
2010-01-01	42.61
2011-01-01	71.16
2012-01-01	73.01
2013-01-01	77.76
2014-01-01	69.42
2015-01-01	76.12
2016-01-01	77.77