Year Percent 1966-01-01 0.13777000000000000 1967-01-01 0.25908000000000003 1968-01-01 0.24114499999999997 1969-01-01 0.22086799999999998 1970-01-01 0.19514700000000001 1971-01-01 0.17918699999999999 1972-01-01 0.59837900000000000 1973-01-01 1.11806000000000000 1974-01-01 2.98955000000000000 1975-01-01 4.36354000000000000 1976-01-01 5.81936999999999900 1977-01-01 8.21793999999999900 1978-01-01 10.27040000000000000 1979-01-01 10.03010000000000000 1980-01-01 9.82099000000000000 1981-01-01 12.54180000000000000 1982-01-01 12.92590000000000000 1983-01-01 12.51920000000000000 1984-01-01 13.12490000000000000 1985-01-01 16.50030000000000000 1986-01-01 16.23350000000000000 1987-01-01 18.22440000000000000 1988-01-01 18.36670000000000000 1989-01-01 19.80910000000000000 1990-01-01 19.44390000000000000 1991-01-01 20.42420000000000000 1992-01-01 19.01440000000000000 1993-01-01 21.15980000000000000 1994-01-01 23.77670000000000000 1995-01-01 23.66510000000000000 1996-01-01 24.00450000000000000 1997-01-01 25.88510000000000000 1998-01-01 30.58970000000000000 1999-01-01 32.40180000000000000 2000-01-01 39.03310000000000000 2001-01-01 43.70170000000000000 2002-01-01 54.08010000000000000 2003-01-01 60.95860000000000000 2004-01-01 64.25230000000000000 2005-01-01 64.59420000000000000 2006-01-01 77.95930000000000000 2007-01-01 86.41530000000000000 2008-01-01 80.75120000000000000 2009-01-01 90.63220000000000000 2010-01-01 87.11290000000000000 2011-01-01 76.35340000000000000 2012-01-01 78.11730000000000000 2013-01-01 76.32060000000000000 2014-01-01 62.77440000000000000 2015-01-01 63.97770000000000000 2016-01-01 59.43780000000000000