Year	% of total
1971	0.24294272027486682
1972	0.22008270337114327
1973	0.23450441511238357
1974	0.25447809662122073
1975	0.26972401164455007
1976	0.2833956433377909
1977	0.28626099302875546
1978	0.28043400261258455
1979	0.32889564684203487
1980	0.3718318720674509
1981	0.41990280831815513
1982	0.4671500545893565
1983	0.5224038156115778
1984	0.49409789929088976
1985	0.48778884641497244
1986	0.515577753030333
1987	0.5192652735517735
1988	0.505053080246396
1989	0.4968061820063093
1990	0.5168503912762517
1991	0.5456884492184176
1992	0.6066657164378515
1993	0.5922992909311962
1994	0.6305458094107408
1995	0.7029033181224832
1996	0.6956288964687557
1997	0.7250508473720365
1998	0.7487766186251155
1999	0.8165360547915032
2000	0.858329344825759
2001	0.8871715035069495
2002	0.8913677070680274
2003	0.9093320076955143
2004	0.916962724602007
2005	0.9742713055050829
2006	1.0283947308420638
2007	1.1243228741690934
2008	1.3272833699141617
2009	1.6426824707724725
2010	1.9309104719775891
2011	2.2005601888343382
2012	2.5917314225486523
2013	3.1820905486447804
2014	3.6291026813594036
2015	4.2390566956531055