Year Percent 1963-01-01 0.56079200000000000 1964-01-01 0.47931599999999996 1965-01-01 0.47347700000000004 1966-01-01 0.57163800000000000 1967-01-01 0.71184200000000000 1968-01-01 1.00321000000000000 1969-01-01 1.37434000000000000 1970-01-01 1.35807000000000000 1971-01-01 1.56351000000000000 1972-01-01 1.73387999999999990 1973-01-01 2.26059000000000000 1974-01-01 3.07270000000000000 1975-01-01 3.82266999999999960 1976-01-01 4.92178000000000000 1977-01-01 5.84864000000000050 1978-01-01 6.65537000000000000 1979-01-01 7.19393000000000000 1980-01-01 7.04007000000000000 1981-01-01 7.04078999999999900 1982-01-01 7.61778000000000100 1983-01-01 7.61778000000000100 1984-01-01 7.61778000000000100 1985-01-01 7.61778000000000100 1986-01-01 7.61778000000000100 1987-01-01 7.61778000000000100 1988-01-01 7.61778000000000100 1989-01-01 7.61778000000000100 1990-01-01 7.61778000000000100 1991-01-01 7.61778000000000100 1992-01-01 10.86330000000000000 1993-01-01 11.22750000000000000 1994-01-01 11.87060000000000000 1995-01-01 12.31620000000000000 1996-01-01 12.22610000000000000 1997-01-01 12.33910000000000000 1998-01-01 12.63900000000000100 1999-01-01 12.48050000000000000 2000-01-01 9.24691000000000000 2001-01-01 6.24574000000000050 2002-01-01 6.43321000000000000 2003-01-01 5.82271999999999950 2004-01-01 4.35837000000000000 2005-01-01 3.02619000000000000 2006-01-01 2.52033000000000000 2007-01-01 2.47715000000000000 2008-01-01 2.48662000000000030 2009-01-01 2.65834000000000000 2010-01-01 3.04094000000000000 2011-01-01 3.47489000000000030 2012-01-01 3.58721000000000000 2013-01-01 3.69054000000000000 2014-01-01 3.73012000000000000 2015-01-01 3.96021000000000000 2016-01-01 3.99026999999999980