Year	% of total
1960	28.444017563117452
1961	28.63247863247863
1962	29.16762342135476
1963	28.716839829122936
1964	29.080646801586497
1965	28.335196571641514
1966	28.836520451278474
1967	28.729501671708324
1968	29.858721909084252
1969	30.406936644004332
1970	27.259960311402835
1971	26.23419012647899
1972	26.77226406734603
1973	27.573296906225497
1974	27.687486334815247
1975	27.133429759537155
1976	25.103338299166992
1977	25.083247687564235
1978	25.906804342070426
1979	27.5631195062652
1980	27.233391771420045
1981	29.6389510890686
1982	28.914737394170974
1983	33.08772443046769
1984	35.28819141722367
1985	36.46175327370844
1986	35.19573341073178
1987	35.526634173320886
1988	38.523050409306336
1989	39.058513279791775
1990	27.73350634304582
1991	26.97838530692513
1992	33.267568854671005
1993	31.193190241414488
1994	33.085522634459984
1995	31.995508986995773
1996	30.619967728922948
1997	30.04534561805678
1998	28.09558808733273
1999	31.300311111111114
2000	32.816514401440145
2001	33.61903729678036
2002	35.02437546746447
2003	34.62705179682794
2004	35.86631551741962
2005	36.314054900323555
2006	38.482374166161314
2007	41.16439444214019
2008	38.51486188425586
2009	36.884044957774464
2010	35.435049032258064
2011	38.399758189398455
2012	36.52642481341001
2013	31.333218997361477
2014	31.457837837837836
2015	32.04726611796982
2016	29.20094883328648