Year	Percent
1979-01-01	70.4753801833334
1980-01-01	72.1752468833334
1981-01-01	72.1599500750000
1982-01-01	71.7546151000000
1983-01-01	71.2912498666667
1984-01-01	71.0211847916666
1985-01-01	71.2175194916667
1986-01-01	72.0080203000000
1987-01-01	71.2965418000000
1988-01-01	71.0394655750000
1989-01-01	72.0944739666667
1990-01-01	72.1037886833333
1991-01-01	69.6577325583333
1992-01-01	69.3863682333334
1993-01-01	68.7258400583333
1994-01-01	70.5762595666667
1995-01-01	71.6403225083333
1996-01-01	71.6626889166667
1997-01-01	70.0564819333334
1998-01-01	69.8691353333333
1999-01-01	69.9244230916667
2000-01-01	70.1821186750000
2001-01-01	70.6721835500000
2002-01-01	69.9768727416667
2003-01-01	70.2240566333333
2004-01-01	70.1420703750000
2005-01-01	70.8126045833334
2006-01-01	70.8025809666667
2007-01-01	70.7617575916667
2008-01-01	70.7545302166667
2009-01-01	69.1045873916666
2010-01-01	68.4257435416667
2011-01-01	68.1440977750000
2012-01-01	67.5219191083333
2013-01-01	66.8277493333334
2014-01-01	66.5782063750000
2015-01-01	67.2843251750000
2016-01-01	66.7885186250000
2017-01-01	66.8752382666666