Year	% of total
1971	21.377163150913145
1972	17.38501077025364
1973	17.14128529278114
1974	13.411683819017364
1975	12.585392758890846
1976	11.585739069478302
1977	11.042501580356692
1978	11.95743350902795
1979	12.59232293637537
1980	11.648576327213476
1981	11.3498176077474
1982	11.402186719572818
1983	11.781451760193324
1984	12.190184347194984
1985	12.185381511447298
1986	13.056581544847734
1987	12.743003725019463
1988	11.976655890345194
1989	10.431194039258319
1990	10.441690250363532
1991	10.570421115593899
1992	11.81246324439498
1993	11.919168388590236
1994	11.700255936802293
1995	12.929519761167144
1996	12.950104862147786
1997	15.605157526308796
1998	13.019713557949938
1999	13.955940646432502
2000	13.390814601531712
2001	13.104775373861276
2002	12.283237954565235
2003	13.147300140278176
2004	13.093976594584946
2005	12.942989104268483
2006	13.320281813800136
2007	13.946999869445575
2008	14.293868480053051
2009	13.16127008671356
2010	9.881002391226067
2011	11.246548877794618
2012	13.050805210787662
2013	13.082296596600967
2014	13.011526633561054
2015	13.019842588222