Year Percent 1960-01-01 14.200000000000000 1961-01-01 16.950000000000000 1962-01-01 20.750000000000000 1963-01-01 11.725000000000000 1964-01-01 9.816670000000000 1965-01-01 9.600000000000000 1966-01-01 10.150000000000000 1967-01-01 11.266700000000000 1968-01-01 13.507100000000000 1969-01-01 15.950000000000000 1970-01-01 12.137200000000000 1971-01-01 11.796800000000000 1972-01-01 11.594300000000000 1973-01-01 11.188500000000000 1974-01-01 13.482000000000001 1975-01-01 9.670060000000001 1976-01-01 7.135550000000000 1977-01-01 9.272710000000000 1978-01-01 10.843200000000000 1979-01-01 12.762700000000000 1980-01-01 14.833800000000000 1981-01-01 18.849300000000000 1982-01-01 19.131800000000000 1983-01-01 15.132500000000000 1984-01-01 12.789600000000000 1985-01-01 9.462539999999999 1986-01-01 11.769900000000000 1987-01-01 12.912300000000000 1988-01-01 11.267700000000000 1989-01-01 18.502200000000000 1990-01-01 8.018610000000000 1991-01-01 8.478850000000000 1992-01-01 11.624200000000000 1993-01-01 15.049600000000000 1994-01-01 16.831800000000000 1995-01-01 18.236200000000000 1996-01-01 17.767700000000000 1997-01-01 18.457600000000000 1998-01-01 20.610600000000000 1999-01-01 22.581800000000000 2000-01-01 21.763000000000000 2001-01-01 20.566600000000000 2002-01-01 15.005300000000000 2003-01-01 10.698200000000000 2004-01-01 8.865750000000000 2005-01-01 9.164620000000000 2006-01-01 10.004400000000000 2007-01-01 10.908300000000000 2008-01-01 10.831500000000000 2009-01-01 11.445500000000000 2010-01-01 10.656800000000000 2011-01-01 11.460999999999999 2012-01-01 12.937100000000000 2013-01-01 13.379400000000000 2014-01-01 12.285600000000000 2015-01-01 12.428500000000000 2016-01-01 11.966500000000000