Year	% of total
1960	100
1961	100
1962	100
1963	100
1964	100
1965	100
1966	100
1967	5.2
1968	7.374631268436578
1969	0.6789351438270502
1970	3.535353535353535
1971	2.78691362298771
1972	3.4552845528455287
1973	3.854902430264575
1974	5.478169261383589
1975	8.060899327274873
1976	10.949782669009526
1977	19.457313037723363
1978	18.8364290974552
1979	25.333066212561356
1980	24.443561208267088
1981	35.56860013928962
1982	38.518150174042766
1983	39.87341772151899
1984	34.864053114132155
1985	35.49761292691884
1986	35.28452759878891
1987	34.0227587267415
1988	37.86959818043973
1989	35.857056329497276
1990	31.838032490974733
1991	28.37602113821138
1992	34.52415325285044
1993	44.269510860820596
1994	41.86254502855469
1995	30.40015693832599
1996	20.32062656641604
1997	18.359761817065685
1998	22.81980441264162
1999	17.814797674418607
2000	55.18717885024841
2001	36.34238520673177
2002	10.516651039543417
2003	27.942589587559162
2004	26.643932533187854
2005	26.190604575163402
2006	26.115223118722213
2007	25.684872047991497
2008	22.469178617157493
2009	26.93441595622853
2010	17.40034516644147
2011	17.918295454545454
2012	41.19401752688784
2013	36.683942965779465
2014	39.85748150565709
2015	21.655407647907644
2016	26.238556101473982