Year Percent 1960-01-01 1.8762500000000000 1961-01-01 1.8391900000000000 1962-01-01 2.2402599999999997 1963-01-01 2.2402599999999997 1964-01-01 2.2402599999999997 1965-01-01 2.2402599999999997 1966-01-01 2.2402599999999997 1967-01-01 3.3743600000000000 1968-01-01 3.5395199999999996 1969-01-01 4.0489000000000000 1970-01-01 3.7535700000000000 1971-01-01 4.5021100000000000 1972-01-01 5.3853599999999995 1973-01-01 6.5571399999999995 1974-01-01 7.3738000000000000 1975-01-01 6.7427899999999990 1976-01-01 5.8116800000000000 1977-01-01 6.5929000000000000 1978-01-01 7.7509100000000000 1979-01-01 8.1368100000000000 1980-01-01 7.8520800000000000 1981-01-01 9.1373000000000000 1982-01-01 8.3272700000000000 1983-01-01 7.0308699999999990 1984-01-01 9.7129400000000000 1985-01-01 11.6247000000000000 1986-01-01 12.4790000000000010 1987-01-01 12.0374000000000000 1988-01-01 12.7658000000000000 1989-01-01 13.7006000000000000 1990-01-01 14.3402000000000000 1991-01-01 12.5998000000000000 1992-01-01 12.5022000000000000 1993-01-01 12.0084000000000000 1994-01-01 9.7453899999999990 1995-01-01 8.6834899999999990 1996-01-01 7.2784400000000000 1997-01-01 5.9736100000000000 1998-01-01 4.6867800000000010 1999-01-01 4.6549800000000000 2000-01-01 5.4386600000000000 2001-01-01 5.9036700000000000 2002-01-01 6.3550600000000000 2003-01-01 6.5804399999999990 2004-01-01 7.7486700000000000 2005-01-01 7.8534800000000000 2006-01-01 7.7327699999999995 2007-01-01 8.9780400000000000 2008-01-01 9.7664000000000000 2009-01-01 10.1631000000000000 2010-01-01 10.8392000000000000 2011-01-01 11.1510000000000000 2012-01-01 11.0384000000000000 2013-01-01 12.3609999999999990 2014-01-01 13.1850000000000000 2015-01-01 14.1190000000000020 2016-01-01 13.7382000000000000