Year Percent 1960-01-01 7.2436100000000000 1961-01-01 7.1866600000000010 1962-01-01 7.2327000000000000 1963-01-01 7.7424300000000010 1964-01-01 8.8340700000000000 1965-01-01 9.1016500000000000 1966-01-01 9.3123200000000000 1967-01-01 9.5712200000000000 1968-01-01 9.8289000000000000 1969-01-01 11.2960000000000000 1970-01-01 6.8955800000000010 1971-01-01 7.2176200000000000 1972-01-01 7.3652700000000000 1973-01-01 7.2189600000000010 1974-01-01 7.6401699999999995 1975-01-01 8.5565199999999990 1976-01-01 8.9487399999999990 1977-01-01 11.1683000000000000 1978-01-01 14.4679000000000000 1979-01-01 16.1538000000000000 1980-01-01 14.6248000000000000 1981-01-01 13.2850000000000000 1982-01-01 14.7880000000000000 1983-01-01 15.6143000000000000 1984-01-01 15.4476000000000000 1985-01-01 15.9608000000000000 1986-01-01 16.1770000000000000 1987-01-01 15.9478000000000000 1988-01-01 16.7269000000000000 1989-01-01 16.1843000000000000 1990-01-01 14.9712000000000000 1991-01-01 10.9161000000000000 1992-01-01 6.9811700000000000 1993-01-01 7.2703899999999990 1994-01-01 8.1180399999999990 1995-01-01 16.5275000000000000 1996-01-01 24.2539000000000000 1997-01-01 22.6594000000000000 1998-01-01 22.8477000000000000 1999-01-01 23.5768000000000000 2000-01-01 22.8354000000000000 2001-01-01 23.2372000000000000 2002-01-01 22.7782000000000000 2003-01-01 23.2525000000000000 2004-01-01 23.7135000000000000 2005-01-01 25.5652000000000000 2006-01-01 26.7110000000000000 2007-01-01 26.5606000000000000 2008-01-01 25.5734000000000000 2009-01-01 22.1174000000000000 2010-01-01 20.8040000000000020 2011-01-01 24.2489000000000000 2012-01-01 25.1442000000000000 2013-01-01 25.7112000000000000 2014-01-01 25.3620000000000000 2015-01-01 27.9038000000000000 2016-01-01 36.7295000000000000