Year	% of total
1960	0.08658008658008658
1961	0.0757002271006813
1962	0.2136752136752137
1963	0.5000937675814215
1964	0.3902547806210626
1965	0.3775355895082651
1966	0.6339306492902025
1967	0.580923076923077
1968	0.5460562603419746
1969	0.5499920521379749
1970	1.2683201803833146
1971	1.4364063724209977
1972	1.2919896640826873
1973	2.2561867864809284
1974	3.358163229578796
1975	4.2862034129000355
1976	4.798497806671506
1977	6.838304327210973
1978	9.709702172213735
1979	12.467967335223973
1980	14.166394483442819
1981	13.528045275007067
1982	13.655449842236406
1983	14.757353611375148
1984	19.111569123926145
1985	19.198549796758634
1986	19.3561653633416
1987	18.975303326316144
1988	18.778161695415935
1989	18.95865488197459
1990	19.5565447300291
1991	20.296781884517237
1992	20.05512209146698
1993	19.9012421864144
1994	20.12514981857586
1995	19.98925803422026
1996	20.72847025759837
1997	21.1991025778815
1998	21.83445890785693
1999	23.025667100210402
2000	23.310712697088114
2001	23.625651640744135
2002	23.534131323002637
2003	24.664933671298268
2004	23.096702350212894
2005	21.587794911299714
2006	23.913753126152816
2007	25.58212927921484
2008	26.50574727257701
2009	28.273751859142298
2010	27.946939820922335
2011	36.10848171944531
2012	38.71858887484006
2013	38.468144946275125
2014	41.514935644545794
2015	39.58721719828527