Year	% of total
1960	59.82356647763075
1961	56.86531014027225
1962	52.63625221980441
1963	47.80299698948009
1964	44.62326635165889
1965	42.87298367989082
1966	40.641244048399074
1967	37.08006467453141
1968	35.601937254339596
1969	33.82547550690831
1970	29.844510159305543
1971	25.898883637099296
1972	23.480880210728056
1973	23.429985544214283
1974	25.044742774092033
1975	24.549144227486714
1976	22.94561445977568
1977	21.886799851000845
1978	19.347889586680296
1979	19.99693016116654
1980	23.69033106944525
1981	26.630533399603955
1982	26.974951830443157
1983	26.020952183383468
1984	27.6972103473024
1985	29.715059427715314
1986	28.15106524473788
1987	27.66805940177169
1988	28.181666512188336
1989	27.04222834054421
1990	26.543930035879036
1991	26.91364280158457
1992	26.06839378238342
1993	26.41742939278698
1994	26.98647634443737
1995	27.750997024190177
1996	28.28452315318277
1997	29.477746062572933
1998	28.74765922651934
1999	30.04550249165873
2000	31.046202375417387
2001	31.990629580905843
2002	32.41775412810592
2003	33.1311269308592
2004	36.3351196855725
2005	34.56886597683347
2006	35.73434904978744
2007	36.19127703121433
2008	37.41059726462117
2009	35.166517013103764
2010	37.96002223029548
2011	33.803969822714635
2012	33.95303125648847
2013	36.70344476167816
2014	36.670901854371955
2015	37.87329741853576
2016	37.0312561145306