Year Percent 1960-01-01 68.1875228424286 1961-01-01 68.1939978893899 1962-01-01 67.4652650071247 1963-01-01 66.2339455594164 1964-01-01 65.3982534147162 1965-01-01 64.9199563716870 1966-01-01 64.9833155369268 1967-01-01 65.1325593198126 1968-01-01 65.2113587838259 1969-01-01 64.8465602520252 1970-01-01 64.6695414651862 1971-01-01 64.2857545478434 1972-01-01 63.6177818152694 1973-01-01 63.9875026511755 1974-01-01 62.9594985126942 1975-01-01 62.0382498705908 1976-01-01 61.8810556757713 1977-01-01 62.0450879551149 1978-01-01 62.1482450728625 1979-01-01 62.2943585833703 1980-01-01 62.2062007330588 1981-01-01 62.1084793865900 1982-01-01 62.0700057627371 1983-01-01 62.3501523806433 1984-01-01 62.0014559543168 1985-01-01 61.6862723939969 1986-01-01 61.4003431756017 1987-01-01 61.1349615497692 1988-01-01 61.3272566482719 1989-01-01 61.7434400386239 1990-01-01 62.2379211058714 1991-01-01 62.7171138059745 1992-01-01 62.7444100875755 1993-01-01 62.2831285874774 1994-01-01 61.8351537723566 1995-01-01 61.4748696726417 1996-01-01 61.4053161299254 1997-01-01 61.5658190933798 1998-01-01 60.7806710749694 1999-01-01 60.0107723493443 2000-01-01 59.5605557031092 2001-01-01 58.9504635419001 2002-01-01 57.9809988096516 2003-01-01 57.6752500209223 2004-01-01 57.6498868846832 2005-01-01 57.8028177138213 2006-01-01 57.9637145011078 2007-01-01 58.1175869396361 2008-01-01 57.8396251618770 2009-01-01 56.9079319438444 2010-01-01 56.7158659810312 2011-01-01 56.6298608854374 2012-01-01 56.5345514387308 2013-01-01 56.9820309722192 2014-01-01 57.3818967756728 2015-01-01 57.6489914576005 2016-01-01 58.2175121365128 2017-01-01 58.8256441034923