Year	% of total
1971	17.963858092075274
1972	14.997892400053717
1973	14.832271098470123
1974	12.412738945510364
1975	11.731690701843107
1976	10.657596007507138
1977	10.554425193704677
1978	11.752626559067533
1979	11.185348401577398
1980	10.073101625705014
1981	10.509256987910378
1982	12.122953344872345
1983	15.650867164061676
1984	16.187852255441847
1985	15.434945624899225
1986	16.282661236886632
1987	17.66422481820181
1988	18.960176552929166
1989	18.51604677661079
1990	25.874107627073172
1991	26.189437020822048
1992	27.39631490378121
1993	26.138404742625486
1994	27.155655704497317
1995	31.15138165398988
1996	31.742067420253896
1997	34.083903545337996
1998	34.60491296546792
1999	33.89809578502993
2000	35.954001359850245
2001	36.511029078750674
2002	38.08632441287609
2003	38.902581670124356
2004	40.32636443180097
2005	40.795930598070065
2006	41.53685300869373
2007	42.12917456027446
2008	44.21705138236422
2009	43.717294752624596
2010	43.43492353278384
2011	42.08349075952678
2012	41.52140519809037
2013	40.16472582127165
2014	40.16384986640098
2015	42.59130817242556