Year Percent 1960-01-01 39.31350000000000 1961-01-01 38.00930000000000 1962-01-01 36.73010000000000 1963-01-01 35.50920000000000 1964-01-01 34.84000000000000 1965-01-01 34.44890000000000 1966-01-01 34.04190000000000 1967-01-01 34.35090000000000 1968-01-01 34.28630000000000 1969-01-01 33.39480000000000 1970-01-01 31.64370000000000 1971-01-01 31.80350000000000 1972-01-01 33.94260000000000 1973-01-01 37.52510000000000 1974-01-01 40.49250000000000 1975-01-01 36.69440000000000 1976-01-01 32.83530000000000 1977-01-01 31.76320000000000 1978-01-01 30.08720000000000 1979-01-01 29.03500000000000 1980-01-01 29.01840000000000 1981-01-01 31.49240000000000 1982-01-01 34.23200000000000 1983-01-01 34.71170000000000 1984-01-01 35.84630000000000 1985-01-01 36.65710000000000 1986-01-01 39.41440000000000 1987-01-01 56.52450000000000 1988-01-01 71.55610000000000 1989-01-01 76.65660000000000 1990-01-01 81.50830000000000 1991-01-01 82.19330000000000 1992-01-01 68.15240000000000 1993-01-01 55.06280000000000 1994-01-01 55.40300000000000 1995-01-01 55.75820000000000 1996-01-01 61.13560000000000 1997-01-01 69.96300000000001 1998-01-01 82.37420000000000 1999-01-01 88.59800000000000 2000-01-01 90.11900000000000 2001-01-01 96.00930000000000 2002-01-01 97.80780000000000 2003-01-01 99.21110000000000 2004-01-01 103.71100000000000 2005-01-01 109.90600000000000 2006-01-01 118.66400000000000 2007-01-01 129.74100000000000 2008-01-01 149.33000000000000 2009-01-01 165.22600000000000 2010-01-01 162.87900000000000 2011-01-01 157.76500000000000 2012-01-01 149.47299999999998 2013-01-01 145.93700000000000 2014-01-01 139.07399999999998 2015-01-01 134.52600000000000 2016-01-01 136.15100000000000