Year	Percent of Total
1960-01-01	38.7313432835821
1961-01-01	39.4599056603774
1962-01-01	40.4391098004884
1963-01-01	41.4167284491474
1964-01-01	42.0534951477579
1965-01-01	42.2624647224835
1966-01-01	42.9470032600518
1967-01-01	43.2820869280778
1968-01-01	43.3984156197487
1969-01-01	43.4712877483962
1970-01-01	43.5519908335720
1971-01-01	43.1396279814549
1972-01-01	42.7195385201444
1973-01-01	42.2605377521817
1974-01-01	41.7405373771451
1975-01-01	41.1293841248532
1976-01-01	40.6577029527849
1977-01-01	40.1040000000000
1978-01-01	39.5159522840414
1979-01-01	38.9252989117922
1980-01-01	38.3322774308384
1981-01-01	37.6474783797438
1982-01-01	37.0129679615069
1983-01-01	36.4103382722141
1984-01-01	35.8283303819519
1985-01-01	35.2554556389255
1986-01-01	35.3851208502371
1987-01-01	35.4771902762305
1988-01-01	35.5765109301329
1989-01-01	35.6979927007299
1990-01-01	35.8376755777073
1991-01-01	34.7720279720280
1992-01-01	33.7949719441083
1993-01-01	32.9168578136385
1994-01-01	32.0872686810348
1995-01-01	31.2856081248452
1996-01-01	30.8580624396524
1997-01-01	30.3394129417912
1998-01-01	29.7380916300450
1999-01-01	29.1426715468889
2000-01-01	28.6059321511750
2001-01-01	27.5763925054804
2002-01-01	26.7638920228495
2003-01-01	26.1261785589570
2004-01-01	25.5498148232820
2005-01-01	24.9481655097809
2006-01-01	24.7515586834562
2007-01-01	24.3894064088789
2008-01-01	23.8813047217873
2009-01-01	23.3143660610321
2010-01-01	22.7821235162190
2011-01-01	22.4121784959819
2012-01-01	22.1227718480793
2013-01-01	21.9393090066297
2014-01-01	21.8231925708281
2015-01-01	21.7447888886518
2016-01-01	22.0348516364563
2017-01-01	22.2384073804321