Year	% of total
1960	2.1942687342323763
1961	2.444786229777257
1962	2.5394540914974852
1963	2.284161454788524
1964	2.118472361939083
1965	1.9324080588661772
1966	2.4744895489220804
1967	2.9009724854188854
1968	4.018944274626789
1969	5.244533827610144
1970	6.571300420796988
1971	8.063106287145867
1972	9.512676813242892
1973	11.175351991594725
1974	13.050903507602118
1975	13.882022860681564
1976	12.906916886253455
1977	12.19608951858205
1978	11.423009389839809
1979	11.13417685774618
1980	9.448537542001596
1981	8.05292953591758
1982	7.765751793664341
1983	8.067517851885778
1984	8.443713851228498
1985	7.35167109083405
1986	7.368386588369343
1987	7.584839380803592
1988	7.231984995522857
1989	8.040198573876802
1990	8.839330399220321
1991	8.48931177580771
1992	7.978765984150063
1993	8.386666546816752
1994	8.957305358446622
1995	9.355916883289762
1996	10.162365782575833
1997	11.489278005700825
1998	12.280166947612317
1999	13.956872340824876
2000	14.345742019986787
2001	14.976738284356921
2002	15.402865715718686
2003	16.91851691024154
2004	18.2164694361415
2005	20.513803465306914
2006	21.15519245769034
2007	22.3145393819931
2008	23.938677662095305
2009	23.401957582905194
2010	23.187447315653355
2011	22.382846050480705
2012	19.376241980724284
2013	16.67400386638524
2014	14.804089392279304
2015	16.19117440746163