Year	% of total
1960	80.48977612543442
1961	79.74693021862834
1962	78.27821293878735
1963	78.0883502736513
1964	76.99359464065346
1965	74.86090338019743
1966	71.68399168399169
1967	66.40279249516924
1968	63.01493074293937
1969	59.81670778991893
1970	65.99790466212677
1971	60.985550203779184
1972	58.276117038132455
1973	54.77767740640369
1974	52.07343626286619
1975	49.28741670314704
1976	46.89275893675527
1977	44.23093873953284
1978	43.178510540978834
1979	43.7890708058686
1980	42.22569341833073
1981	43.550230726895556
1982	44.49134655972984
1983	41.537765344742475
1984	40.5795931546658
1985	42.434308589923766
1986	42.504718844651244
1987	42.40858160340484
1988	42.13559480860235
1989	40.63132530120482
1990	35.739924354790865
1991	36.709766072811775
1992	35.42448448275862
1993	32.781899623158615
1994	32.25284527518173
1995	31.715112310639043
1996	31.921592541909
1997	31.728333040884365
1998	29.18893635571055
1999	28.102479709894666
2000	27.722332051986086
2001	24.959047957371226
2002	25.47717957936365
2003	25.214954490812296
2004	23.68365667671573
2005	21.44107219442459
2006	21.971584926072847
2007	23.032790568139617
2008	22.89541203092589
2009	21.08678302675585
2010	22.65452380952381
2011	23.513826476231078
2012	24.49451300944048
2013	22.91425171736997
2014	21.66084174255476
2015	21.428872752420467
2016	19.9426101618705