Year	% of total
1971	60.92615601930651
1972	55.152074288538465
1973	49.69193955903257
1974	48.51451446144374
1975	48.11791487637304
1976	43.51845178782543
1977	48.63975654619314
1978	51.95612772540799
1979	48.67553679448419
1980	45.24814270926786
1981	44.749972065422355
1982	45.98917236125096
1983	46.14825798367957
1984	49.215646913543
1985	55.19391970991211
1986	58.495642534540146
1987	59.932317397933424
1988	59.973115011044584
1989	60.52302241059283
1990	61.72853508638221
1991	63.66153317789339
1992	64.81633933525995
1993	63.03046335349285
1994	63.80406906652863
1995	62.48844294588755
1996	64.29696352547646
1997	64.45082115752385
1998	64.0396305443207
1999	66.05118049468523
2000	67.1699313391776
2001	66.03904160153218
2002	67.45737576212704
2003	69.78325496434954
2004	69.25529368385612
2005	70.73396441804158
2006	72.46697322999741
2007	73.72713345844888
2008	71.70823468917608
2009	71.40276779763414
2010	70.77772911355697
2011	73.07251364142641
2012	70.36888592000331
2013	70.33121218832244
2014	67.93129704076709
2015	66.15346173861987