Year	Percent
1979-01-01	78.4434323166666
1980-01-01	78.3413116000000
1981-01-01	78.0501423416666
1982-01-01	77.4314808500000
1983-01-01	76.7153284000000
1984-01-01	76.2566518916666
1985-01-01	75.7558696500000
1986-01-01	75.8626607416666
1987-01-01	75.3429539000000
1988-01-01	75.2378754166667
1989-01-01	75.4450234583334
1990-01-01	75.5925557250000
1991-01-01	74.6457740500000
1992-01-01	74.1347235416666
1993-01-01	73.5474140916667
1994-01-01	73.6087114000000
1995-01-01	73.8086486000000
1996-01-01	73.5799253250000
1997-01-01	73.0043146083333
1998-01-01	72.6990795500000
1999-01-01	72.2404837083334
2000-01-01	72.0947548500000
2001-01-01	71.8630007833333
2002-01-01	71.7906070833334
2003-01-01	71.5415656500000
2004-01-01	71.5114659333333
2005-01-01	72.0868699083333
2006-01-01	72.2371818000000
2007-01-01	72.5097942666666
2008-01-01	72.6201342750000
2009-01-01	72.3048880666666
2010-01-01	72.3606824333334
2011-01-01	72.1731282833334
2012-01-01	71.7279338416667
2013-01-01	71.3923016750000
2014-01-01	70.9573759250000
2015-01-01	71.0973009500000
2016-01-01	70.6085508250000
2017-01-01	70.6847453916667