Year	% of total
1971	49.04975360923323
1972	45.160039223102
1973	48.793773360176914
1974	45.139942758903246
1975	45.3013953890063
1976	44.06019271118026
1977	45.917530924476516
1978	46.78200961582424
1979	47.718331855585745
1980	48.25348219133051
1981	50.32531473347195
1982	50.19558669613081
1983	57.905852586124105
1984	57.71715300289828
1985	59.852358622304806
1986	59.064838697986666
1987	51.76917102349595
1988	51.07409288792033
1989	48.410800366549324
1990	45.06439280684118
1991	44.656420511318714
1992	43.71352886989096
1993	41.15708305645212
1994	39.61296113873663
1995	38.94273486011665
1996	38.5732460304129
1997	38.278873061979155
1998	36.37233136551518
1999	34.036135544344695
2000	35.35409873996357
2001	31.632172519808456
2002	31.6854717888088
2003	27.804752910269293
2004	28.162582562863065
2005	23.256107585382367
2006	23.27853370487493
2007	23.310417109515917
2008	24.10133823104503
2009	23.166149659954414
2010	23.25319523997735
2011	25.79599674122003
2012	26.503896670114695
2013	28.599976170814678
2014	24.810559920280546
2015	20.2848170531346