Year	% of total
1971	10.832508523039701
1972	10.212486419565932
1973	11.29839218924564
1974	13.18266110338433
1975	14.1456826696872
1976	14.594953243898898
1977	13.982107278196665
1978	13.610360570204044
1979	13.828562508536752
1980	9.554466727438468
1981	11.697183492916736
1982	5.56846670448515
1983	5.164957370567157
1984	6.366331173307597
1985	6.486467885962045
1986	7.200607200607201
1987	7.22554505112869
1988	6.848633692915099
1989	5.634797561836914
1990	0.867177337765573
1991	0.8806262230919765
1992	0.8906649508102342
1993	0.6376376717700413
1994	0.8409118155817021
1995	0.9806025588113908
1996	1.1437882894881155
1997	0.9810486319821853
1998	0.9532062391681109
1999	0.6655340638102215
2000	0.5102110792610168
2001	0.51997736886063
2002	0.5052964010790184
2003	0.44435857805255025
2004	0.4153240243465807
2005	0.39789579036018113
2006	0.30841322590671094
2007	0.13103322546830137
2008	0.15727234527882827
2009	0.1911015288122305
2010	0.23326144036009003
2011	0.20051627178021572
2012	0.13035403232318574
2013	0.091851920751558
2014	0.12339005358653755
2015	0.11377941318872857