Year	Percent of Total
1960-01-01	31.8033619625535
1961-01-01	32.0904684140400
1962-01-01	32.2370875558177
1963-01-01	32.2397904627854
1964-01-01	32.1288556981085
1965-01-01	31.9258639522721
1966-01-01	31.6705922508643
1967-01-01	31.3201262353455
1968-01-01	30.9004619463964
1969-01-01	30.4540896608147
1970-01-01	30.0113176831200
1971-01-01	29.5116523046072
1972-01-01	29.0820283058739
1973-01-01	28.7018286306012
1974-01-01	28.3314394735757
1975-01-01	27.9544201547384
1976-01-01	27.7411630163098
1977-01-01	27.4643516677793
1978-01-01	27.1786180528966
1979-01-01	26.9594292766162
1980-01-01	26.8388506719359
1981-01-01	26.7755587116358
1982-01-01	26.8116658817583
1983-01-01	26.9074287587560
1984-01-01	26.9932909786636
1985-01-01	27.0366681111831
1986-01-01	27.1074056203971
1987-01-01	27.1358552180801
1988-01-01	27.1128996306812
1989-01-01	27.0336994193290
1990-01-01	26.8872565131478
1991-01-01	26.7823116756501
1992-01-01	26.5550936692744
1993-01-01	26.2384475693168
1994-01-01	25.8855282773361
1995-01-01	25.5218619535454
1996-01-01	25.0086703882722
1997-01-01	24.5565672494822
1998-01-01	24.1119419874718
1999-01-01	23.6102348977777
2000-01-01	23.0421829068083
2001-01-01	22.5197519740193
2002-01-01	21.9383720367566
2003-01-01	21.3383161478938
2004-01-01	20.8034849050233
2005-01-01	20.3783600166028
2006-01-01	20.0652500644228
2007-01-01	19.8320709148237
2008-01-01	19.6812893842565
2009-01-01	19.5997505579642
2010-01-01	19.5867060328230
2011-01-01	19.6623477646762
2012-01-01	19.7996881141425
2013-01-01	19.9905711890977
2014-01-01	20.2013571968555
2015-01-01	20.3980792082655
2016-01-01	20.6083509141985
2017-01-01	20.7608677847762