Year	Percent
1973-01-01	28.6997
1974-01-01	32.2905
1975-01-01	35.1138
1976-01-01	37.1478
1977-01-01	37.5779
1978-01-01	38.5716
1979-01-01	37.2667
1980-01-01	36.1205
1981-01-01	38.8576
1982-01-01	42.7213
1983-01-01	42.7213
1984-01-01	42.7213
1985-01-01	42.7213
1986-01-01	42.7213
1987-01-01	51.8435
1988-01-01	51.1132
1989-01-01	54.3161
1990-01-01	55.0975
1991-01-01	53.5973
1992-01-01	50.7363
1993-01-01	50.9800
1994-01-01	50.5048
1995-01-01	50.3798
1996-01-01	46.4412
1997-01-01	45.4451
1998-01-01	46.8324
1999-01-01	46.9948
2000-01-01	52.3800
2001-01-01	57.8698
2002-01-01	61.0858
2003-01-01	59.8916
2004-01-01	60.2593
2005-01-01	61.0124
2006-01-01	60.8108
2007-01-01	60.6241
2008-01-01	61.7809
2009-01-01	64.6237
2010-01-01	69.6325
2011-01-01	78.8736
2012-01-01	79.9639
2013-01-01	80.4966
2014-01-01	81.2232
2015-01-01	84.6377
2016-01-01	86.0368