Year	Percent of Total
1960-01-01	55.3338271751640
1961-01-01	54.1361932599486
1962-01-01	52.8500701300525
1963-01-01	51.6085088908195
1964-01-01	50.5887935466013
1965-01-01	49.8666172552295
1966-01-01	49.2266393420336
1967-01-01	48.8875115974202
1968-01-01	48.7812689256656
1969-01-01	48.8019623776683
1970-01-01	48.8938352856698
1971-01-01	49.2455115910490
1972-01-01	49.6030552212863
1973-01-01	49.9648300556444
1974-01-01	50.3672679337216
1975-01-01	50.8326759433607
1976-01-01	51.0795539911757
1977-01-01	51.4367632613309
1978-01-01	51.8575745210980
1979-01-01	52.2681727378624
1980-01-01	52.6197869469887
1981-01-01	52.8617098481936
1982-01-01	53.0087496962750
1983-01-01	53.0748395110529
1984-01-01	53.0947521617274
1985-01-01	53.0899960311068
1986-01-01	52.9151322845239
1987-01-01	52.7534031620056
1988-01-01	52.5973833808894
1989-01-01	52.4534433647268
1990-01-01	52.3479634076546
1991-01-01	52.0226214533856
1992-01-01	51.8275020643375
1993-01-01	51.7478192257076
1994-01-01	51.7619535225690
1995-01-01	51.8635102672952
1996-01-01	52.1232609743672
1997-01-01	52.4069971733733
1998-01-01	52.7603957094444
1999-01-01	53.2448029284602
2000-01-01	53.8752341661834
2001-01-01	54.5739494636189
2002-01-01	55.4226259086978
2003-01-01	56.3494801560072
2004-01-01	57.2380457097077
2005-01-01	58.0224522976941
2006-01-01	58.8131772943210
2007-01-01	59.4253665036208
2008-01-01	59.9136794146102
2009-01-01	60.3679682326041
2010-01-01	60.8193670722084
2011-01-01	61.0023299793793
2012-01-01	61.2356226881042
2013-01-01	61.4514719040271
2014-01-01	61.5653711789610
2015-01-01	61.5569169919324
2016-01-01	61.4482897499940
2017-01-01	61.2822867588434