Year	% of total
1971	42.22402988671969
1972	38.57706052527086
1973	39.80850596186604
1974	36.36245076814732
1975	38.76707864907013
1976	36.441980860743605
1977	38.4309801067443
1978	42.83340446203997
1979	40.322280426516336
1980	38.66571435690023
1981	37.469205773445175
1982	34.197989850298974
1983	32.88821613083682
1984	31.39730394866216
1985	27.427640983201318
1986	26.40522427207789
1987	21.390263468628035
1988	23.691879502292075
1989	22.8579417109978
1990	24.478362461227334
1991	22.79518630816649
1992	20.72655339417108
1993	19.531377738364117
1994	21.167924301392226
1995	17.13543879526035
1996	15.55873065315971
1997	15.795319435218055
1998	16.476989623841938
1999	14.814482291074995
2000	13.070663240229742
2001	12.529859513644842
2002	11.207006692852767
2003	12.415090107046773
2004	13.232922655415056
2005	15.07847345652101
2006	15.556279271734747
2007	15.525709629985807
2008	13.768174879619972
2009	12.33356081203355
2010	12.565651367753844
2011	13.362232628781168
2012	11.08936475612373
2013	12.388660500171293
2014	11.080157256574646
2015	9.982039097500802