Year	Percent of Total
1960-01-01	39.1626820462760
1961-01-01	39.4756151650851
1962-01-01	39.6886260830235
1963-01-01	39.8724138398568
1964-01-01	40.1067817696773
1965-01-01	40.4148936632609
1966-01-01	40.8291625228403
1967-01-01	41.2788253773320
1968-01-01	41.7268473972890
1969-01-01	42.1098090683539
1970-01-01	42.3964834062506
1971-01-01	42.6879894060932
1972-01-01	42.8799326410640
1973-01-01	42.9924312253696
1974-01-01	43.0595457283553
1975-01-01	43.1021271352726
1976-01-01	43.1261696517036
1977-01-01	43.1119448755495
1978-01-01	43.0690499808750
1979-01-01	43.0031703235253
1980-01-01	42.9216313891105
1981-01-01	42.9003043423763
1982-01-01	42.8341294762570
1983-01-01	42.7473335307895
1984-01-01	42.6668232974480
1985-01-01	42.6046726696206
1986-01-01	42.7209223670611
1987-01-01	42.8500831858501
1988-01-01	42.9666537521347
1989-01-01	43.0278150110017
1990-01-01	43.0089488336096
1991-01-01	43.1299881279237
1992-01-01	43.1217181865723
1993-01-01	43.0198366486349
1994-01-01	42.8723523029509
1995-01-01	42.6976331383492
1996-01-01	42.4645444942703
1997-01-01	42.2267319633078
1998-01-01	41.9501117189818
1999-01-01	41.5809890085478
2000-01-01	41.0986275700869
2001-01-01	40.6299542002529
2002-01-01	40.0382054733130
2003-01-01	39.3768414310243
2004-01-01	38.7324146456798
2005-01-01	38.1549873667130
2006-01-01	37.6248524028541
2007-01-01	37.2096016880470
2008-01-01	36.8670716259430
2009-01-01	36.5332040942575
2010-01-01	36.1833109441687
2011-01-01	35.9802207162627
2012-01-01	35.7192116376177
2013-01-01	35.4427770953356
2014-01-01	35.2045969862922
2015-01-01	35.0193480572101
2016-01-01	34.8903251616446
2017-01-01	34.7780970328012