Year Percent 1973-01-01 6.7774500000000000 1974-01-01 4.8792599999999995 1975-01-01 6.9020600000000005 1976-01-01 7.6236100000000000 1977-01-01 12.2907000000000000 1978-01-01 16.6890000000000000 1979-01-01 20.7191000000000000 1980-01-01 30.5462000000000000 1981-01-01 40.9086000000000000 1982-01-01 57.5107000000000000 1983-01-01 61.1485000000000000 1984-01-01 60.2751000000000000 1985-01-01 58.1469000000000000 1986-01-01 52.4863000000000000 1987-01-01 46.6297000000000000 1988-01-01 40.6974000000000000 1989-01-01 40.1885000000000000 1990-01-01 41.4102000000000000 1991-01-01 38.0811000000000000 1992-01-01 38.1689000000000000 1993-01-01 41.9772000000000000 1994-01-01 43.3381000000000000 1995-01-01 43.1762000000000000 1996-01-01 48.2129000000000000 1997-01-01 51.0928000000000000 1998-01-01 54.7938000000000000 1999-01-01 58.1007000000000000 2000-01-01 58.4583000000000000 2001-01-01 61.6391000000000000 2002-01-01 63.1873000000000000 2003-01-01 62.6548000000000000 2004-01-01 59.6134000000000000 2005-01-01 60.7789000000000000 2006-01-01 59.3324000000000000 2007-01-01 63.3292000000000000 2008-01-01 74.5478000000000000 2009-01-01 74.5427000000000000 2010-01-01 65.4002000000000000 2011-01-01 66.7943000000000000 2012-01-01 71.5401000000000000 2013-01-01 74.9241000000000000 2014-01-01 77.8245000000000000 2015-01-01 80.6895000000000000 2016-01-01 82.4176000000000000