Year Percent 1960-01-01 14.3913000000000000 1961-01-01 12.3773000000000000 1962-01-01 12.2853000000000000 1963-01-01 11.2413000000000000 1964-01-01 9.8647900000000000 1965-01-01 8.8069000000000000 1966-01-01 7.4304200000000000 1967-01-01 7.3665899999999995 1968-01-01 7.7217899999999995 1969-01-01 7.9349399999999990 1970-01-01 7.4466700000000000 1971-01-01 6.6570000000000000 1972-01-01 7.4885100000000010 1973-01-01 7.8282000000000000 1974-01-01 7.3578800000000010 1975-01-01 8.2098700000000000 1976-01-01 8.7184700000000000 1977-01-01 9.6766399999999990 1978-01-01 11.8842000000000000 1979-01-01 14.7548000000000000 1980-01-01 10.3761000000000000 1981-01-01 9.9991000000000000 1982-01-01 8.6617900000000000 1983-01-01 7.7850500000000000 1984-01-01 6.2990200000000000 1985-01-01 6.5830500000000000 1986-01-01 10.3582000000000000 1987-01-01 13.1194000000000000 1988-01-01 16.9595000000000000 1989-01-01 22.4795000000000000 1990-01-01 24.1334000000000000 1991-01-01 25.0839000000000000 1992-01-01 23.1036000000000000 1993-01-01 19.6673000000000000 1994-01-01 11.9952000000000000 1995-01-01 5.5778800000000000 1996-01-01 3.8239199999999998 1997-01-01 3.8019000000000000 1998-01-01 9.2394800000000000 1999-01-01 12.4279000000000000 2000-01-01 10.9764000000000000 2001-01-01 12.5191000000000000 2002-01-01 15.7415000000000000 2003-01-01 17.1083000000000000 2004-01-01 15.4434000000000000 2005-01-01 13.8141000000000000 2006-01-01 12.2640000000000010 2007-01-01 12.2596000000000000 2008-01-01 13.8528000000000000 2009-01-01 17.1122000000000000 2010-01-01 17.3199000000000000 2011-01-01 16.7605000000000000 2012-01-01 17.2443000000000000 2013-01-01 17.5189000000000000 2014-01-01 17.9224000000000000 2015-01-01 20.0886000000000000 2016-01-01 22.5592000000000000