Year	% of total
1960	44.02514942036108
1961	43.84420161992258
1962	44.521243830745775
1963	44.737027461959656
1964	44.24718263103758
1965	43.72954252127808
1966	42.66610870587032
1967	42.40575225981107
1968	41.906572198272265
1969	39.706152405619804
1970	37.556245703557664
1971	36.985720981115605
1972	35.23044673007723
1973	35.35572576247799
1974	33.705705924400505
1975	33.95454300372611
1976	35.5078413100476
1977	35.282023575856485
1978	34.256130198857335
1979	35.787150391185776
1980	38.21849149328032
1981	38.75353769037945
1982	39.65211374707983
1983	40.10034895834498
1984	39.40368686593192
1985	40.046980792852224
1986	39.46769041514605
1987	39.741096627445614
1988	39.50919761689422
1989	38.45817823310813
1990	39.43331635182437
1991	39.089620151691804
1992	38.8914397491678
1993	38.49807990888821
1994	37.92029790095
1995	37.41156217932144
1996	37.74266797552039
1997	37.78242255308496
1998	37.80163197770899
1999	37.20184070704156
2000	38.18488653378574
2001	37.61476551336567
2002	37.510356870683566
2003	38.21950348503268
2004	37.189036659081545
2005	37.078213773676296
2006	36.847462292612455
2007	36.683474489258685
2008	36.02543472203704
2009	34.22002160033008
2010	34.036247202571786
2011	33.233952542526495
2012	31.973174087512035
2013	32.463260701898136
2014	31.918740540070047
2015	29.367138508357232