Year Percent 1966-01-01 27.0153 1967-01-01 26.0282 1968-01-01 26.5855 1969-01-01 27.2623 1970-01-01 28.6497 1971-01-01 22.9027 1972-01-01 25.9424 1973-01-01 27.5543 1974-01-01 11.5631 1975-01-01 14.1621 1976-01-01 17.1079 1977-01-01 21.8978 1978-01-01 24.4537 1979-01-01 24.4537 1980-01-01 24.4537 1981-01-01 24.4537 1982-01-01 24.4537 1983-01-01 24.4537 1984-01-01 24.4537 1985-01-01 24.4537 1986-01-01 24.4537 1987-01-01 24.4537 1988-01-01 24.4537 1989-01-01 24.4537 1990-01-01 24.4537 1991-01-01 24.4537 1992-01-01 24.4537 1993-01-01 24.4537 1994-01-01 24.4537 1995-01-01 24.4537 1996-01-01 24.4537 1997-01-01 24.4537 1998-01-01 24.4537 1999-01-01 24.4537 2000-01-01 24.4537 2001-01-01 24.4537 2002-01-01 61.4841 2003-01-01 52.5496 2004-01-01 43.9403 2005-01-01 42.4027 2006-01-01 42.9483 2007-01-01 45.3989 2008-01-01 41.8897 2009-01-01 56.2388 2010-01-01 52.8087 2011-01-01 46.4411 2012-01-01 49.9099 2013-01-01 57.0696 2014-01-01 63.2337 2015-01-01 84.3989 2016-01-01 92.4086