Year	% of total
1971	15.54925386397311
1972	17.42621181252917
1973	18.207014913679398
1974	18.52179428992754
1975	18.06933610633571
1976	18.900361861972648
1977	19.448959843538944
1978	19.50364852349332
1979	20.18504163570326
1980	19.986113580682947
1981	20.266432364841894
1982	21.25058942888338
1983	21.200061788591047
1984	22.22605695713369
1985	21.70799995203245
1986	22.476160392052172
1987	23.120132845193062
1988	23.390667127379043
1989	23.086778279409526
1990	29.125577871973515
1991	28.828017794383403
1992	27.065923509551254
1993	26.089790013232072
1994	25.360915744905597
1995	26.29546591523416
1996	27.04543629557411
1997	27.797701646698016
1998	28.889832207489547
1999	29.661783670518684
2000	29.647643686215154
2001	30.150295908553414
2002	30.52040677269612
2003	30.946025605624943
2004	31.270188105709792
2005	32.39174665003983
2006	33.115723048205226
2007	34.16251574291968
2008	34.60493347945766
2009	33.92098801337802
2010	34.170701583190294
2011	28.005971870778072
2012	28.879053853570525
2013	32.43552669880098
2014	32.565838219539174