Year	% of total
1971	0.148314827375275
1972	0.15518746504129122
1973	0.16812858319136328
1974	0.18789426111999027
1975	0.2044232624349979
1976	0.2181012471009199
1977	0.22679603028691428
1978	0.21892762530781948
1979	0.26854033601825184
1980	0.31146074262911855
1981	0.3642526586492544
1982	0.41314306045854415
1983	0.4675224188906384
1984	0.4343729429509175
1985	0.43414182288065895
1986	0.455710566489693
1987	0.45924253992242714
1988	0.4487912913502784
1989	0.44218697399171103
1990	0.4815856203865288
1991	0.5169552434839371
1992	0.5948232014358986
1993	0.5910098939538755
1994	0.6333403552479013
1995	0.7094972758758392
1996	0.6936804686832302
1997	0.7260394257759168
1998	0.7424344268315648
1999	0.8104578719207581
2000	0.8485365618779881
2001	0.9022674803519714
2002	0.9067493743927011
2003	0.9184958649791184
2004	0.932484055642079
2005	0.9966067219265613
2006	1.044348279786966
2007	1.17241830008656
2008	1.398573035527928
2009	1.7486413028339622
2010	2.0385628277986294
2011	2.358106041309592
2012	2.79128828600512
2013	3.3948476943316526
2014	3.8893172028031784
2015	4.558857158521133