Year	% of total
1971	8.084405921152394
1972	7.802512577886185
1973	7.864992448230545
1974	7.808869836434268
1975	7.764707406178345
1976	7.555241769557661
1977	8.360663500507908
1978	8.279668834358276
1979	9.607437403792405
1980	11.345642713999899
1981	10.786269300994968
1982	11.866309903178845
1983	11.556001066229033
1984	12.253846290027942
1985	12.303593953544908
1986	12.427143492239924
1987	12.98319159087828
1988	13.704056073706383
1989	14.87653857033853
1990	20.5165794848516
1991	20.860136343168094
1992	20.664888473236655
1993	21.202830149066067
1994	21.968425403438985
1995	22.551751858612974
1996	22.536810202608944
1997	22.74008009911078
1998	23.752422010817845
1999	25.316314644453776
2000	25.64854477516442
2001	27.258241282486033
2002	28.830433922152714
2003	30.858341989469363
2004	31.427378879894587
2005	31.383573985871227
2006	31.13486301769036
2007	32.416371178880816
2008	33.02217842231166
2009	33.84776909508058
2010	33.899580351358196
2011	32.27546846221701
2012	31.269439147431434
2013	30.93646138445576
2014	31.697908186833423
2015	32.510075501332956