Year	% of total
1960	15.541905762547485
1961	16.734052111410605
1962	17.4934725848564
1963	17.109721136304405
1964	17.60004701181172
1965	18.713730182470837
1966	20.671220671220674
1967	23.873340397681233
1968	25.616118006835762
1969	27.49970626248384
1970	22.718700890518598
1971	26.54951569364315
1972	28.308862364001264
1973	30.121449362641773
1974	32.06650831353919
1975	33.27496473563889
1976	33.17140238313473
1977	35.60599382988101
1978	36.209405796498814
1979	33.795449712949186
1980	34.01021657449233
1981	32.18746031074045
1982	31.00042211903757
1983	35.21474411716307
1984	36.05505327736519
1985	34.300072398960864
1986	32.096922874325095
1987	32.44593068704942
1988	31.15775664152181
1989	31.460240963855423
1990	34.380164639572826
1991	33.12513865220759
1992	36.107305172413795
1993	38.30940904419322
1994	33.60464693665628
1995	34.313874281734286
1996	31.789866575436193
1997	33.63936831022987
1998	32.31563731473409
1999	31.692859609739248
2000	30.95101043382757
2001	29.570479573712255
2002	27.599728563724607
2003	26.310709256397047
2004	27.396827451675833
2005	29.671508220157257
2006	30.825016227912013
2007	32.06752692164872
2008	31.44920988119932
2009	33.56562081939799
2010	33.07039682539683
2011	32.5972926881262
2012	33.275724153810735
2013	35.113594210009815
2014	38.7548560177209
2015	39.40883817427386
2016	38.85470098920864