Year	Percent of Total
1960-01-01	22.0412793848194
1961-01-01	22.1209087622702
1962-01-01	22.2257600835911
1963-01-01	22.3240279284110
1964-01-01	22.3657430235905
1965-01-01	22.3261655243784
1966-01-01	22.2729127435942
1967-01-01	22.1287535104774
1968-01-01	21.9288693938592
1969-01-01	21.7384867618706
1970-01-01	21.5948834680324
1971-01-01	21.4239552096919
1972-01-01	21.3451202865523
1973-01-01	21.2955809118501
1974-01-01	21.1789635971094
1975-01-01	20.9597252166082
1976-01-01	20.9849724899191
1977-01-01	20.8195178617701
1978-01-01	20.5620110664760
1979-01-01	20.3705008689213
1980-01-01	20.3263682460235
1981-01-01	20.2776121655638
1982-01-01	20.4601797639938
1983-01-01	20.7696261006293
1984-01-01	21.0466645892703
1985-01-01	21.2223108699754
1986-01-01	21.4266197465097
1987-01-01	21.5119043404410
1988-01-01	21.5218310972703
1989-01-01	21.5057186316126
1990-01-01	21.4568808661658
1991-01-01	21.4840069576982
1992-01-01	21.4198972157576
1993-01-01	21.2643215302112
1994-01-01	21.0310336991896
1995-01-01	20.7393103294315
1996-01-01	20.1761721783506
1997-01-01	19.6317452967470
1998-01-01	19.0821654549367
1999-01-01	18.4928719441549
2000-01-01	17.8565391711892
2001-01-01	17.1458830522365
2002-01-01	16.4789847082005
2003-01-01	15.8378419403454
2004-01-01	15.2290953132165
2005-01-01	14.6799065534687
2006-01-01	14.4624606163068
2007-01-01	14.2359989774930
2008-01-01	14.0612215862655
2009-01-01	14.0072595602778
2010-01-01	14.0893070196635
2011-01-01	14.2049698613090
2012-01-01	14.4082339402257
2013-01-01	14.6629432610213
2014-01-01	14.9122202244404
2015-01-01	15.1309579191263
2016-01-01	15.2409757780902
2017-01-01	15.4055814573748