Year	% of total
1971	0.0277074095978074
1972	0.0263480428356626
1973	0.0252341471492057
1974	0.0242600182708139
1975	0.0229735228869391
1976	0.0220155337721049
1977	0.0213350214816396
1978	0.0202608046714923
1979	0.0196513640471247
1980	0.0187128327678468
1981	0.0180312011111026
1982	0.0168615397366832
1983	0.0159081983447269
1984	0.0153601639519418
1985	0.0179562530877649
1986	0.023537596623002
1987	0.0183684558725251
1988	0.0169417425924151
1989	0.0155918778885781
1990	0.0167829199163046
1991	0.0170736530629407
1997	0.00102261485717126
1998	0.0253777006422848
1999	0.0181050192530061
2000	0.00487998428208954
2001	0.00228741190194423
2002	0.00147242428224741
2003	0.00214479904006254
2004	0.00200813512493065
2005	0.0031235762259575
2006	0.00720047256821779
2007	0.0109863420051595
2008	0.0153093457430433
2009	0.0214806784229616
2010	0.0278039312379346
2011	0.0431300699141821
2012	0.14416405450951
2013	0.260402242471679
2014	0.352086171118935
2015	0.547667837783708