Year	% of total
1960	0
1961	0
1962	0
1963	0
1964	0
1965	0
1966	0
1967	0
1968	0.18117919277029534
1969	1.5931278345760629
1970	1.639344262295082
1971	4.09677681253552
1972	6.995509092247662
1973	8.650541897964578
1974	9.020180828213197
1975	9.189018002874613
1976	8.465460249873942
1977	7.0385914186149385
1978	7.7822318085625914
1979	6.399052558188399
1980	4.747953783897607
1981	8.698498127204624
1982	7.7273448099659925
1983	9.240063096950891
1984	19.546847746939193
1985	22.32500378133533
1986	29.212028574102376
1987	31.123026107415953
1988	36.41545921607111
1989	38.12907608695652
1990	35.890110180812925
1991	35.91493321443111
1992	35.59795788130185
1993	36.065594863579925
1994	34.37682564542393
1995	33.48812773255393
1996	32.492140858881555
1997	29.23546236525031
1998	30.504364192934556
1999	28.591555454072882
2000	28.15757669031011
2001	27.33462909807051
2002	26.265750238624193
2003	24.04658917349687
2004	22.991339299914696
2005	19.87907892691185
2006	20.341563424024468
2007	18.25575886482529
2008	18.963720906302054
2009	18.07694547896488
2010	20.779699651381065
2011	19.79810175863453
2012	20.912288818882637
2013	20.155270123825257
2014	20.84204707054763
2015	20.61866432438659