Year	% of total
1960	36.46864466619593
1961	40.03429973461519
1962	44.77706129380178
1963	38.21049208757859
1964	45.94646600702849
1965	40.3588458131514
1966	38.16700206654453
1967	42.68432489776363
1968	40.76624809370843
1969	38.47468722723305
1970	30.552641974635954
1971	29.369453766145437
1972	22.567625189105204
1973	19.657220505402503
1974	19.001643055548122
1975	20.28398113268643
1976	28.365807332274347
1977	27.183654074602043
1978	28.47818877269009
1979	29.78055383438198
1980	27.351656380679962
1981	21.435257410296412
1982	23.96792450119942
1983	20.452737177468773
1984	16.31660018657815
1985	13.272359978280795
1986	9.635219497854804
1987	8.312834380860796
1988	7.488365895159803
1989	9.10133966406796
1990	8.49067231704774
1991	9.566619133238266
1992	8.202412551004215
1993	5.269624021087864
1994	5.087095679877284
1995	5.406340785136838
1996	6.08178175818996
1997	5.162533060531962
1998	7.355509732566345
1999	6.35258049601237
2000	5.766241143232982
2001	4.38320441016274
2002	4.875277712551704
2003	5.21207328888129
2004	4.788908230908548
2005	5.375431102396667
2006	4.636901333258405
2007	5.001578680365118
2008	4.647311366697022
2009	4.526224741502611
2010	4.6634236245868665
2011	3.1112109638283534
2012	3.7011244261355416
2013	4.290238174162653
2014	2.1570289856371336
2015	2.1604489133868325