Year	% of total
1971	23.154848046309695
1972	19.528178243774576
1973	20.706455542021924
1974	24.70449172576832
1975	28.016359918200408
1976	31.135531135531135
1977	29.890848026868177
1978	30.32984714400644
1979	28.955223880597014
1980	31.33826496301278
1981	21.935483870967744
1982	23.002577319587626
1983	21.611940298507463
1984	19.841269841269842
1985	19.631901840490798
1986	15.723830734966594
1987	19.267241379310345
1988	13.477088948787062
1989	7.818765036086608
1990	10.936238902340598
1991	12.738139708629062
1992	10.2803738317757
1993	8.064992614475628
1994	4.507512520868113
1995	5.376078914919852
1996	4.283903675538657
1997	5.736782902137233
1998	6.474993959893695
1999	15.585255442983401
2000	13.501367721766314
2001	11.345702708466623
2002	0.5722178374112076
2003	0.5714285714285714
2004	0.5883401675878053
2005	0.5651595744680852
2006	0.45425048669695006
2007	0.5313330207844975
2008	0.6040471156750227
2009	0.43078690407811604
2010	0.4374917141720801
2011	0.38508309687880016
2012	0.4752143123369363
2013	0.4980811627337307
2014	0.4591368227731864
2015	0.34439574201628054