Year	% of total
1960	0.03104036114007888
1961	0.05816558184174646
1962	0.10494382824849248
1963	0.15118710852608444
1964	0.4980186760014679
1965	0.6821691048036966
1966	0.786593231589375
1967	0.9568728051380991
1968	0.9571488552127478
1969	1.381250843339386
1970	1.5648641968832346
1971	1.9253422983200905
1972	2.786191263925095
1973	3.0224493788997546
1974	3.3948843024184994
1975	5.65487503827698
1976	6.064905661701434
1977	7.241884414337344
1978	8.233095000617165
1979	8.863022337316645
1980	10.473722594266889
1981	14.96462057889695
1982	16.214994422342617
1983	18.73351378990988
1984	23.193413113032353
1985	26.829284022224897
1986	28.805313779927182
1987	29.028949102154417
1988	30.394132561575315
1989	31.234732186127072
1990	32.276620063976516
1991	32.59605345583629
1992	32.87139172446959
1993	33.81241769155718
1994	33.15220525018997
1995	33.13092761593317
1996	33.612212624332166
1997	33.76471894240809
1998	32.850372371101024
1999	33.10829218789641
2000	32.67972365904369
2001	32.830535442819176
2002	33.10700592540955
2003	32.32026769017114
2004	32.26305055438121
2005	31.640344642029444
2006	31.072370672240325
2007	29.493618753668745
2008	29.784873873761658
2009	29.270497832510184
2010	28.902361722120336
2011	28.842524342305037
2012	27.95115748135582
2013	27.97017663519562
2014	28.77238145992716
2015	26.480265337191213