Year Percent 1960-01-01 86.35030000000000 1961-01-01 87.73090000000000 1962-01-01 87.79880000000000 1963-01-01 82.96560000000000 1964-01-01 74.26810000000000 1965-01-01 69.66220000000000 1966-01-01 69.81700000000000 1967-01-01 67.20560000000000 1968-01-01 64.08950000000000 1969-01-01 62.11610000000000 1970-01-01 60.28990000000000 1971-01-01 61.67910000000000 1972-01-01 63.68480000000000 1973-01-01 64.36800000000000 1974-01-01 67.91950000000000 1975-01-01 69.69490000000000 1976-01-01 68.42260000000000 1977-01-01 67.02890000000000 1978-01-01 66.27199999999999 1979-01-01 65.63710000000000 1980-01-01 64.62850000000000 1981-01-01 63.44330000000000 1982-01-01 62.91980000000000 1983-01-01 62.86820000000000 1984-01-01 62.78450000000000 1985-01-01 63.64970000000000 1986-01-01 58.84300000000000 1987-01-01 54.21960000000000 1988-01-01 57.04060000000000 1989-01-01 58.83520000000000 1990-01-01 69.06570000000000 1991-01-01 75.49620000000000 1992-01-01 80.37320000000000 1993-01-01 85.27380000000000 1994-01-01 86.91200000000000 1995-01-01 85.14730000000000 1996-01-01 82.97910000000000 1997-01-01 86.17040000000000 1998-01-01 88.70890000000000 1999-01-01 90.49880000000000 2000-01-01 91.64540000000000 2001-01-01 93.13010000000000 2002-01-01 94.74710000000000 2003-01-01 94.67790000000000 2004-01-01 94.62210000000000 2005-01-01 95.50920000000000 2006-01-01 96.44910000000000 2007-01-01 97.08920000000000 2008-01-01 97.73960000000000 2009-01-01 98.26370000000000 2010-01-01 98.64240000000000 2011-01-01 98.92520000000000 2012-01-01 99.19670000000000 2013-01-01 99.26650000000000 2014-01-01 99.31140000000000 2015-01-01 99.35799999999999 2016-01-01 99.35370000000000