Year	% of total
1971	25.295439479294757
1972	23.981557206766528
1973	22.992173002345822
1974	22.429335055232844
1975	22.82004257461183
1976	21.26298865006235
1977	22.01170090745653
1978	22.623707935076236
1979	21.47589252281544
1980	20.52880855734317
1981	19.387413411026582
1982	19.5521443004519
1983	19.727687446468696
1984	20.442409942228377
1985	22.202800437159244
1986	22.82793122800377
1987	23.756202254540508
1988	23.895757447708842
1989	24.278595294901585
1990	34.0240732777962
1991	35.155724294934
1992	37.169892932474895
1993	37.79780716905351
1994	40.38470763895684
1995	40.86957277964915
1996	42.0798509392277
1997	42.35681431290134
1998	42.1141579773624
1999	42.94814434612585
2000	44.1352118176852
2001	44.21823603371274
2002	45.66866030775221
2003	48.09712391540626
2004	48.56694084710072
2005	50.2530889972574
2006	52.32615367957602
2007	53.97369329211511
2008	53.33258610101858
2009	53.568669500977826
2010	53.53391731786515
2011	56.05263273479625
2012	54.29695751971851
2013	55.03749270300358
2014	53.34859345725271
2015	52.26638440219412