Year	% of total
1960	31.781808955981223
1961	30.833803297429345
1962	30.850618510002835
1963	31.668590748887286
1964	32.24926175615316
1965	32.1892306045227
1966	31.82719005737476
1967	31.496017677602055
1968	29.768476866828735
1969	28.795536276409745
1970	27.005606931960358
1971	25.43889329367344
1972	24.66096970456448
1973	25.39820301281322
1974	26.035969151982542
1975	26.148098770240434
1976	27.64879920890554
1977	27.210677100449647
1978	27.979081537019685
1979	28.885520807461784
1980	30.937143593593632
1981	32.8421147944417
1982	33.399831922899104
1983	34.963823043289885
1984	35.47086355576386
1985	36.238002303427145
1986	35.363693018490544
1987	35.88000603817975
1988	35.98032984461147
1989	36.29056667724936
1990	36.77671786732274
1991	36.72781060670661
1992	36.636111696241954
1993	36.607518693691446
1994	36.316544114893276
1995	35.89295562620687
1996	36.15768571920706
1997	35.38463090236284
1998	35.31357665408625
1999	35.41204441830205
2000	35.8520935840773
2001	35.450802626429535
2002	36.830598731534316
2003	36.34364158081006
2004	36.66565584151999
2005	36.89271809981793
2006	37.02272456148415
2007	36.77636355084342
2008	37.360511311550255
2009	35.70114527429718
2010	35.44897447926614
2011	35.35906575665591
2012	32.848111009431925
2013	32.468819078494946
2014	32.342900042723485
2015	29.15700635587693
2016	27.071413869706095