Year Percent 1960-01-01 23.2800 1961-01-01 23.2246 1962-01-01 19.8177 1963-01-01 17.4801 1964-01-01 13.2669 1965-01-01 13.5406 1966-01-01 14.6993 1967-01-01 16.0775 1968-01-01 14.1694 1969-01-01 16.4482 1970-01-01 18.7199 1971-01-01 22.5778 1972-01-01 26.6139 1973-01-01 26.9682 1974-01-01 22.4305 1975-01-01 29.3345 1976-01-01 25.5924 1977-01-01 28.0348 1978-01-01 37.2616 1979-01-01 31.1744 1980-01-01 31.1744 1981-01-01 31.1744 1982-01-01 31.1744 1983-01-01 31.1744 1984-01-01 31.1744 1985-01-01 31.1744 1986-01-01 31.1744 1987-01-01 31.1744 1988-01-01 31.1744 1989-01-01 31.1744 1990-01-01 31.1744 1991-01-01 31.1744 1992-01-01 31.1744 1993-01-01 31.1744 1994-01-01 31.1744 1995-01-01 31.1744 1996-01-01 31.1744 1997-01-01 31.1744 1998-01-01 31.1744 1999-01-01 31.1744 2000-01-01 53.8199 2001-01-01 47.3705 2002-01-01 35.7074 2003-01-01 31.8967 2004-01-01 28.2813 2005-01-01 25.4315 2006-01-01 24.1554 2007-01-01 26.0874 2008-01-01 36.0465 2009-01-01 65.4688 2010-01-01 51.8115 2011-01-01 129.5900 2012-01-01 57.5096 2013-01-01 99.1645 2014-01-01 99.1645 2015-01-01 305.6600 2016-01-01 293.2680