Year Percent 1960-01-01 32.777700000000000 1961-01-01 31.802600000000000 1962-01-01 33.543300000000000 1963-01-01 33.314800000000000 1964-01-01 33.790200000000000 1965-01-01 36.186300000000000 1966-01-01 37.858500000000000 1967-01-01 40.010999999999996 1968-01-01 40.184900000000000 1969-01-01 41.212100000000000 1970-01-01 41.928900000000000 1971-01-01 43.663600000000000 1972-01-01 45.669000000000000 1973-01-01 46.457600000000000 1974-01-01 46.557900000000000 1975-01-01 49.699500000000000 1976-01-01 52.504200000000000 1977-01-01 56.330400000000000 1978-01-01 60.731200000000000 1979-01-01 63.637400000000000 1980-01-01 68.042200000000000 1981-01-01 71.214400000000000 1982-01-01 72.125800000000000 1983-01-01 71.702800000000000 1984-01-01 72.372100000000000 1985-01-01 74.755300000000000 1986-01-01 76.460500000000000 1987-01-01 76.199500000000000 1988-01-01 78.885000000000000 1989-01-01 81.698500000000000 1990-01-01 84.892900000000000 1991-01-01 87.095500000000000 1992-01-01 88.685900000000000 1993-01-01 90.174800000000000 1994-01-01 89.093900000000000 1995-01-01 89.610900000000000 1996-01-01 92.329800000000000 1997-01-01 95.908100000000000 1998-01-01 95.908100000000000 1999-01-01 95.908100000000000 2000-01-01 98.345100000000000 2001-01-01 88.749400000000000 2002-01-01 87.687999999999990 2003-01-01 86.850700000000000 2004-01-01 85.586500000000000 2005-01-01 88.841300000000000 2006-01-01 91.805900000000000 2007-01-01 90.499300000000000 2008-01-01 93.000300000000000 2009-01-01 97.288100000000000 2010-01-01 96.518500000000000 2011-01-01 95.228500000000000 2012-01-01 93.591000000000010 2013-01-01 92.036900000000000 2014-01-01 88.360300000000000 2015-01-01 84.693700000000000 2016-01-01 83.146400000000000