Year	% of total
1971	27.56258234519104
1972	26.756318108045445
1973	23.21391158600461
1974	18.952524491333836
1975	17.363510711817554
1976	14.638665843113033
1977	10.226063829787234
1978	10.850084766287237
1979	11.911508282476024
1980	13.891929545228383
1981	14.33336421754841
1982	12.637922254286199
1983	13.583633798401005
1984	24.8726902371599
1985	24.979925053533194
1986	25.305312751844276
1987	28.236036966879052
1988	29.325134353038447
1989	24.37834069254009
1990	17.331421619742787
1991	16.601385959626395
1992	14.874313585047238
1993	14.027461930395232
1994	16.685421994884912
1995	13.686155470502836
1996	10.088299362066284
1997	6.691083737885044
1998	7.996903361828993
1999	11.535572486318275
2000	10.058479532163743
2001	9.927691182263237
2002	7.143530552600034
2003	6.442034433980298
2004	7.085217053133051
2005	6.2789544349424835
2006	7.171323611265724
2007	6.655318101644858
2008	7.628756352184538
2009	5.998982784927976
2010	5.186479252480247
2011	5.896731773351382
2012	6.739047930883086
2013	7.651718853904646
2014	9.078518197044803
2015	9.275061116551095