Year	Percent of Total
1960-01-01	63.4475443034219
1961-01-01	62.6357288873550
1962-01-01	61.8298767942867
1963-01-01	60.9798600124773
1964-01-01	60.1806060178490
1965-01-01	59.4660798979631
1966-01-01	58.0787873245233
1967-01-01	56.9658052493321
1968-01-01	55.9531703567665
1969-01-01	54.9777248531027
1970-01-01	54.0914368203201
1971-01-01	53.7576359746462
1972-01-01	53.4041497582506
1973-01-01	53.0956940958922
1974-01-01	52.9538760035405
1975-01-01	53.0299334595196
1976-01-01	53.8389785615066
1977-01-01	54.8685301110686
1978-01-01	56.0164092404617
1979-01-01	57.1105415705214
1980-01-01	58.0352367308452
1981-01-01	58.9381361352912
1982-01-01	59.5760378055123
1983-01-01	60.0241801095507
1984-01-01	60.4724027121092
1985-01-01	61.0293077491929
1986-01-01	61.1677436747898
1987-01-01	61.6153921381916
1988-01-01	62.2466691353362
1989-01-01	62.9601246010839
1990-01-01	63.7844080938648
1991-01-01	64.9151307609666
1992-01-01	65.9274434405546
1993-01-01	66.8160642651636
1994-01-01	67.5377359170928
1995-01-01	67.9250812249208
1996-01-01	68.5225587409759
1997-01-01	69.0393712171649
1998-01-01	69.4023970336858
1999-01-01	69.6872256735337
2000-01-01	70.0302963660452
2001-01-01	70.3415973129227
2002-01-01	70.7825656196169
2003-01-01	71.2713185728024
2004-01-01	71.6634834567440
2005-01-01	71.8643359045393
2006-01-01	72.6992190161943
2007-01-01	73.3554232027515
2008-01-01	73.8498457965419
2009-01-01	74.3046231223876
2010-01-01	74.7958278673406
2011-01-01	75.2036868103957
2012-01-01	75.7111353781236
2013-01-01	76.2476499874249
2014-01-01	76.7069491995929
2015-01-01	77.0499929620300
2016-01-01	76.8268344345238
2017-01-01	76.5634367759628