Year	% of total
1960	31.25686059275521
1961	29.763313609467453
1962	28.30654420206659
1963	27.873002478772218
1964	25.78053493338757
1965	25.66610769517421
1966	24.86387594197848
1967	24.832829167330043
1968	24.771246614449893
1969	24.984399119781912
1970	28.33765837276751
1971	28.565600046628198
1972	28.53622064687638
1973	29.306114188864434
1974	26.1496975439108
1975	26.17971433737118
1976	27.45546486497828
1977	29.465570400822198
1978	30.78596013464957
1979	30.706938470170194
1980	29.69898168525495
1981	25.87116235172197
1982	25.814789840413578
1983	23.181701832010823
1984	24.67306015693113
1985	25.106607796520624
1986	26.488408373544246
1987	28.96920045628954
1988	26.435157259801812
1989	26.73767488055893
1990	32.11359902682037
1991	30.926630144683244
1992	27.82775378998333
1993	32.998012580754846
1994	30.60984360066035
1995	33.085919821088375
1996	31.87730939895119
1997	33.857189208252514
1998	34.15375691719489
1999	33.2346
2000	30.559708595859586
2001	33.9814121772394
2002	32.49716636392777
2003	29.955878337683195
2004	28.09483820944898
2005	27.419254775075668
2006	28.953511218920557
2007	29.323832434674408
2008	27.86550257325911
2009	29.50632513661202
2010	30.70343612903226
2011	28.069257891602145
2012	28.243931236999874
2013	30.737414248021107
2014	30.548918918918922
2015	32.600585733882035
2016	33.52052431824571