Year	% of total
1960	7.910939413276305
1961	9.089726354135044
1962	12.031543309198177
1963	15.746684126384794
1964	16.732363636363637
1965	19.691854106234246
1966	18.669163328827768
1967	20.712819997279762
1968	24.03561159648316
1969	22.646655477321108
1970	24.026308755584406
1971	24.840758588668052
1972	23.271319278258783
1973	22.279612412572526
1974	20.511084069625944
1975	22.390645300996102
1976	22.60344711957615
1977	23.124840851359828
1978	21.964847611743128
1979	21.824232129431092
1980	22.181323303275306
1981	21.123802694258053
1982	22.996832314011396
1983	22.358090380795918
1984	22.045262122148234
1985	20.278792263373052
1986	18.08131865317048
1987	20.24491786364882
1988	22.34845938818357
1989	24.979878671391674
1990	22.475681529164532
1991	21.87817748067207
1992	22.82352353256618
1993	20.614075475882185
1994	20.0664779465621
1995	21.033562200337496
1996	20.167944020986894
1997	22.593270571827055
1998	26.20515660136491
1999	25.47254056948415
2000	26.773789787250905
2001	28.95418630675845
2002	27.541178858137126
2003	28.371854761832065
2004	26.476790611220856
2005	25.126989447628134
2006	24.413014164899327
2007	24.821232845114068
2008	23.31950128666521
2009	22.042008053867416
2010	23.080005829204314
2011	22.543932160132762
2012	21.424610972102453
2013	20.769340618869737
2014	20.76312543412134
2015	21.067179533053046