Year Percent 1966-01-01 12.149800000000000 1967-01-01 11.093400000000000 1968-01-01 12.346100000000000 1969-01-01 13.810700000000000 1970-01-01 15.140100000000000 1971-01-01 12.894600000000000 1972-01-01 13.699800000000000 1973-01-01 15.987400000000000 1974-01-01 7.953770000000000 1975-01-01 9.507090000000000 1976-01-01 10.312200000000000 1977-01-01 14.044200000000000 1978-01-01 17.037800000000000 1979-01-01 17.037800000000000 1980-01-01 17.037800000000000 1981-01-01 17.037800000000000 1982-01-01 17.037800000000000 1983-01-01 17.037800000000000 1984-01-01 17.037800000000000 1985-01-01 17.037800000000000 1986-01-01 17.037800000000000 1987-01-01 17.037800000000000 1988-01-01 17.037800000000000 1989-01-01 17.037800000000000 1990-01-01 17.037800000000000 1991-01-01 17.037800000000000 1992-01-01 17.037800000000000 1993-01-01 17.037800000000000 1994-01-01 17.037800000000000 1995-01-01 17.037800000000000 1996-01-01 17.037800000000000 1997-01-01 17.037800000000000 1998-01-01 17.037800000000000 1999-01-01 17.037800000000000 2000-01-01 17.037800000000000 2001-01-01 17.037800000000000 2002-01-01 28.648900000000000 2003-01-01 27.019000000000002 2004-01-01 25.700200000000000 2005-01-01 27.744300000000000 2006-01-01 30.488200000000000 2007-01-01 34.380300000000000 2008-01-01 36.174200000000000 2009-01-01 50.027500000000000 2010-01-01 42.687900000000000 2011-01-01 36.064400000000000 2012-01-01 35.802300000000000 2013-01-01 36.966000000000000 2014-01-01 41.838700000000000 2015-01-01 62.718400000000000 2016-01-01 77.692900000000000