Year Percent 1960-01-01 22.86150000000000 1961-01-01 20.51370000000000 1962-01-01 19.74390000000000 1963-01-01 17.95860000000000 1964-01-01 24.55520000000000 1965-01-01 22.17980000000000 1966-01-01 22.34130000000000 1967-01-01 22.87680000000000 1968-01-01 24.32600000000000 1969-01-01 24.34530000000000 1970-01-01 21.70150000000000 1971-01-01 23.87940000000000 1972-01-01 26.38080000000000 1973-01-01 27.38550000000000 1974-01-01 33.77830000000000 1975-01-01 40.98890000000000 1976-01-01 33.05900000000000 1977-01-01 30.76180000000000 1978-01-01 31.29740000000000 1979-01-01 29.94760000000000 1980-01-01 32.04880000000000 1981-01-01 32.38100000000000 1982-01-01 32.27230000000000 1983-01-01 33.41190000000000 1984-01-01 34.90310000000000 1985-01-01 38.56960000000000 1986-01-01 43.36900000000000 1987-01-01 46.36620000000000 1988-01-01 49.76120000000000 1989-01-01 51.70800000000000 1990-01-01 52.38570000000000 1991-01-01 55.02040000000000 1992-01-01 58.29850000000000 1993-01-01 58.77950000000000 1994-01-01 59.66320000000000 1995-01-01 62.84310000000000 1996-01-01 66.66530000000000 1997-01-01 68.58960000000000 1998-01-01 67.87380000000000 1999-01-01 69.45760000000000 2000-01-01 69.22250000000000 2001-01-01 69.68800000000000 2002-01-01 72.87760000000000 2003-01-01 76.54000000000000 2004-01-01 83.03670000000000 2005-01-01 88.60820000000000 2006-01-01 87.15520000000000 2007-01-01 85.03430000000000 2008-01-01 88.96170000000000 2009-01-01 92.29920000000000 2010-01-01 90.23120000000000 2011-01-01 89.66340000000000 2012-01-01 90.21190000000000 2013-01-01 90.35670000000000 2014-01-01 92.87799999999999 2015-01-01 96.24090000000000 2016-01-01 98.56020000000000