Year	% of total
1960	5.038458698029355
1961	7.400125799103412
1962	9.931576757684509
1963	11.417867846214225
1964	15.846878042845495
1965	16.76852193705715
1966	17.237323688507534
1967	18.697493687676044
1968	19.704162673774626
1969	21.715467620729033
1970	22.983091096467692
1971	24.746428416374684
1972	26.15195110871906
1973	28.859710256871672
1974	25.980037934476023
1975	24.132404154357193
1976	26.169396703207443
1977	20.875822809678727
1978	22.43683322493896
1979	21.869083317305783
1980	22.36197515630261
1981	19.326008169635262
1982	16.227050730026928
1983	13.214101156425395
1984	9.350522596917864
1985	8.577759468690509
1986	8.632242459032677
1987	8.837440537881355
1988	8.20648017318325
1989	9.547180552166393
1990	9.615977058488717
1991	10.444497958680792
1992	10.845123011410237
1993	9.883460936042844
1994	9.738529509726291
1995	10.10704392273601
1996	9.315341674126802
1997	9.057418071276755
1998	9.327244584690904
1999	8.505359593083849
2000	7.370175619479672
2001	6.869681678594136
2002	7.499323082807316
2003	6.613493668002593
2004	5.65195460934292
2005	5.475435867592307
2006	5.057011512818824
2007	4.206942992521677
2008	3.9174570889636238
2009	3.718930297729174
2010	3.1385934060736287
2011	2.809452317623916
2012	2.882304839025438
2013	2.4155772520128
2014	2.3624553855660415
2015	2.428865270278769