Year	% of total
1960	18.901062001782122
1961	19.367995489649285
1962	19.6612643192032
1963	20.114779260015208
1964	20.324415440568515
1965	19.239772079042947
1966	20.027583828834867
1967	19.949829734259712
1968	20.958506098567593
1969	21.019107857670548
1970	22.108976005703216
1971	21.14161260528794
1972	19.615276000220124
1973	17.03991873052693
1974	15.861221312007373
1975	14.69066029923653
1976	13.482030309835707
1977	13.276971076011144
1978	12.660895064277856
1979	13.36086476076306
1980	13.551719587291586
1981	13.38736206601456
1982	12.14000397167939
1983	10.57027079676234
1984	10.808265830676557
1985	10.35706286860306
1986	8.773548220801414
1987	9.266230449159904
1988	8.31885309543586
1989	10.645191610761184
1990	10.616250226410063
1991	10.91356744254672
1992	11.603760722063438
1993	11.625636851591683
1994	12.660372575517481
1995	13.351168664843915
1996	11.764817819962495
1997	12.395144917825554
1998	13.378971328456565
1999	13.680667417650106
2000	14.413115656979716
2001	15.708410386113524
2002	16.121242757668302
2003	15.137382497687014
2004	16.126054288926444
2005	16.817576137963773
2006	18.15671176557506
2007	19.32740371535515
2008	19.156715182523293
2009	20.82697378029299
2010	21.570718389649034
2011	22.296610195789253
2012	27.08446058609455
2013	24.700581967958517
2014	24.564620818207512
2015	28.972127775484424