Year	Percent
1961-01-01	5.94579646017699
1977-01-01	1.68776371308017
1978-01-01	1.82798921186695
1979-01-01	1.89629629629630
1980-01-01	2.75282526803825
1981-01-01	4.03871600485847
1982-01-01	5.79420038952608
1983-01-01	7.81645953719096
1984-01-01	8.10310190802607
1985-01-01	7.80288717881186
1986-01-01	7.35562030925120
1987-01-01	7.33459822212853
1988-01-01	7.64332306421355
1989-01-01	7.44066372610796
1990-01-01	7.01587301587302
1991-01-01	7.62057995392548
1992-01-01	8.65934464917854
1993-01-01	9.04152773047094
1994-01-01	9.28341930992564
1995-01-01	9.37981223509618
1996-01-01	9.92045163120341
1997-01-01	9.93756820910983
1998-01-01	11.25000000000000
1999-01-01	12.12500000000000
2000-01-01	11.37500000000000
2001-01-01	10.80000000000000
2002-01-01	10.37500000000000
2003-01-01	9.80000000000000
2004-01-01	10.60000000000000
2005-01-01	10.02500000000000
2006-01-01	9.02500000000000
2007-01-01	8.42500000000000
2008-01-01	7.77500000000000
2009-01-01	9.65000000000000
2010-01-01	12.75000000000000
2011-01-01	17.90000000000000
2012-01-01	24.50000000000000
2013-01-01	27.47500000000000
2014-01-01	26.55000000000000
2015-01-01	24.95000000000000
2016-01-01	23.55000000000000
2017-01-01	21.52500000000000