Year	% of total
1960	6.671180243707189
1961	7.261436058823617
1962	7.690595708399768
1963	8.090390856304891
1964	9.816589881327616
1965	10.295420051770767
1966	11.023441773039051
1967	12.027692799597741
1968	13.064913192185543
1969	15.805711605363088
1970	18.350296532429848
1971	20.671265654912194
1972	22.779702017526645
1973	24.298480348558556
1974	22.76972429022718
1975	21.27203259291871
1976	21.975551227833712
1977	21.3893300915913
1978	21.01622507924708
1979	18.955245551719393
1980	16.59691332782896
1981	14.796901180613183
1982	12.725817618664998
1983	11.406505556564914
1984	10.258392870382526
1985	8.327365547648174
1986	8.380543991005444
1987	7.933469253037427
1988	8.327487605152042
1989	8.915566288495038
1990	8.525419780607573
1991	8.358172096757542
1992	8.070971230514685
1993	7.423449300350339
1994	7.291321089093358
1995	6.758248517493384
1996	6.387520304120435
1997	6.254605059294427
1998	6.294046210702323
1999	5.890334977577889
2000	5.377775147301183
2001	5.337455851711102
2002	5.1218568185651066
2003	5.357770485000093
2004	4.8339038786518715
2005	4.6246158702334546
2006	3.6839115959349384
2007	3.567118917289489
2008	3.0765634327728653
2009	2.743457689968288
2010	2.427403563784738
2011	2.5611375711311335
2012	2.728780527966399
2013	2.3903225520870257
2014	2.15553623224199
2015	2.028558479355731