Year	Percent
1980-01-01	22.58
1981-01-01	21.86
1982-01-01	23.31
1983-01-01	23.86
1984-01-01	23.46
1985-01-01	25.18
1986-01-01	27.44
1987-01-01	28.96
1988-01-01	30.06
1989-01-01	30.91
1990-01-01	31.52
1991-01-01	33.29
1992-01-01	33.41
1993-01-01	34.85
1994-01-01	34.77
1995-01-01	36.59
1996-01-01	37.24
1997-01-01	39.01
1998-01-01	40.11
1999-01-01	40.76
2000-01-01	38.83
2001-01-01	38.41
2002-01-01	38.90
2003-01-01	41.98
2004-01-01	43.09
2005-01-01	42.75
2006-01-01	43.45
2007-01-01	43.76
2008-01-01	39.55
2009-01-01	32.00
2010-01-01	31.97
2011-01-01	32.45
2012-01-01	31.77
2013-01-01	31.39
2014-01-01	31.57
2015-01-01	30.55