Year Percent 1962-01-01 94.39250000000000 1963-01-01 96.51570000000000 1964-01-01 97.07720000000000 1965-01-01 95.91000000000000 1966-01-01 90.79630000000000 1967-01-01 86.23050000000000 1968-01-01 85.51840000000000 1969-01-01 84.96860000000000 1970-01-01 89.36950000000000 1971-01-01 96.85440000000000 1972-01-01 95.62600000000000 1973-01-01 91.39260000000000 1974-01-01 91.83760000000000 1975-01-01 95.86040000000000 1976-01-01 98.06950000000000 1977-01-01 99.38770000000000 1978-01-01 97.30710000000000 1979-01-01 93.27530000000000 1980-01-01 92.55460000000000 1981-01-01 92.40040000000000 1982-01-01 92.41330000000000 1983-01-01 91.76470000000000 1984-01-01 89.84190000000000 1985-01-01 90.30910000000000 1986-01-01 90.53350000000000 1987-01-01 89.45050000000000 1988-01-01 89.70890000000000 1989-01-01 87.59720000000000 1990-01-01 81.91300000000000 1991-01-01 75.99040000000000 1992-01-01 74.41590000000000 1993-01-01 74.34880000000000 1994-01-01 78.56590000000000 1995-01-01 77.43930000000000 1996-01-01 75.93250000000000 1997-01-01 72.06040000000000 1998-01-01 68.66310000000000 1999-01-01 75.30470000000000 2000-01-01 79.36320000000000 2001-01-01 81.84590000000000 2002-01-01 84.30490000000000 2003-01-01 87.85730000000000 2004-01-01 90.17370000000000 2005-01-01 91.77880000000000 2006-01-01 95.99600000000001 2007-01-01 99.28040000000000 2008-01-01 98.72610000000000 2009-01-01 96.16950000000000 2010-01-01 94.11610000000000 2011-01-01 93.50570000000000 2012-01-01 92.78410000000000 2013-01-01 92.66840000000000 2014-01-01 93.22790000000000 2015-01-01 94.05020000000000 2016-01-01 94.88910000000000