Year Percent 1973-01-01 26.799700000000000 1974-01-01 27.733000000000000 1975-01-01 28.470500000000000 1976-01-01 28.200200000000000 1977-01-01 27.311400000000000 1978-01-01 29.316500000000000 1979-01-01 33.352900000000000 1980-01-01 37.209300000000000 1981-01-01 29.216300000000000 1982-01-01 20.326100000000000 1983-01-01 21.203000000000003 1984-01-01 21.501600000000000 1985-01-01 20.813800000000000 1986-01-01 19.084500000000000 1987-01-01 19.550500000000000 1988-01-01 19.211400000000000 1989-01-01 18.560900000000000 1990-01-01 18.374400000000000 1991-01-01 12.994500000000000 1992-01-01 11.980300000000000 1993-01-01 13.218100000000000 1994-01-01 14.252200000000000 1995-01-01 12.851300000000000 1996-01-01 13.879700000000000 1997-01-01 17.104900000000000 1998-01-01 19.781700000000000 1999-01-01 22.928700000000000 2000-01-01 26.371100000000000 2001-01-01 29.519800000000000 2002-01-01 32.496300000000000 2003-01-01 35.014400000000000 2004-01-01 37.587900000000000 2005-01-01 39.688200000000000 2006-01-01 39.504000000000000 2007-01-01 41.474400000000000 2008-01-01 46.461700000000000 2009-01-01 50.006000000000000 2010-01-01 48.513900000000000 2011-01-01 48.881500000000000 2012-01-01 50.506600000000000 2013-01-01 54.074000000000000 2014-01-01 56.630500000000000 2015-01-01 60.063800000000000 2016-01-01 63.692000000000000