Year	Percent of Total
1960-01-01	40.0493246451433
1961-01-01	40.2334627147865
1962-01-01	40.6705962508745
1963-01-01	41.1766171034738
1964-01-01	41.5235454333626
1965-01-01	41.6331237133053
1966-01-01	41.8636609245728
1967-01-01	41.8077930334732
1968-01-01	41.5888923789920
1969-01-01	41.3760632912582
1970-01-01	41.2356498691209
1971-01-01	41.2198406140593
1972-01-01	41.1662642437746
1973-01-01	41.0667934165236
1974-01-01	40.8674312553653
1975-01-01	40.5295349488787
1976-01-01	40.0307379220530
1977-01-01	39.4317979381397
1978-01-01	38.7331652913790
1979-01-01	37.9585994058833
1980-01-01	37.1411237414503
1981-01-01	36.2208654421726
1982-01-01	35.3486585404846
1983-01-01	34.5154145654700
1984-01-01	33.7258806344820
1985-01-01	33.0015723812135
1986-01-01	32.5131335693327
1987-01-01	32.0773347290649
1988-01-01	31.6993847144257
1989-01-01	31.3550121859130
1990-01-01	31.0086593682835
1991-01-01	30.8828676239332
1992-01-01	30.5867939541259
1993-01-01	30.2023942731426
1994-01-01	29.8293155855825
1995-01-01	29.4995305230850
1996-01-01	28.8761600972128
1997-01-01	28.4220877394016
1998-01-01	28.0133584277523
1999-01-01	27.4876520662641
2000-01-01	26.7918048917191
2001-01-01	26.1432720447931
2002-01-01	25.3610600746035
2003-01-01	24.5102414225619
2004-01-01	23.7135560729748
2005-01-01	23.0374357627828
2006-01-01	22.4966654817318
2007-01-01	22.0256731980291
2008-01-01	21.6396965636678
2009-01-01	21.3342735262165
2010-01-01	21.1004120512856
2011-01-01	20.9194270911204
2012-01-01	20.8167283293951
2013-01-01	20.7649827771036
2014-01-01	20.7200796294326
2015-01-01	20.6549080667765
2016-01-01	20.6041638241620
2017-01-01	20.5157945870093