Year	% of total
1971	0.30399312057577726
1972	0.2736403982209908
1973	0.29391948677185825
1974	0.3223965225674285
1975	0.326504738056027
1976	0.3142847464814331
1977	0.3215493734359362
1978	0.31070327182434954
1979	0.34133155786290215
1980	0.3066693821184819
1981	0.3000292785319702
1982	0.32520481177365185
1983	0.36166217000894363
1984	0.31790519053347593
1985	0.31747424603189944
1986	0.38146449247421566
1987	0.41547125955318875
1988	0.39429101874483596
1989	0.3785123445730734
1990	0.4115516864351789
1991	0.46302463056199755
1992	0.5496325251618368
1993	0.5376299296151464
1994	0.5497579450071415
1995	0.6460932578150616
1996	0.6187437501913341
1997	0.6409424006881542
1998	0.6382979042315389
1999	0.6675594441367695
2000	0.6391438905707358
2001	0.6648935189289006
2002	0.6706939736232477
2003	0.6874202729797971
2004	0.6723192180898143
2005	0.7393259868513433
2006	0.7508126519054356
2007	0.8507767755430128
2008	1.0491015863285336
2009	1.3754291904585465
2010	1.7621423610282152
2011	2.055928637443346
2012	2.4803550999473596
2013	3.2001059501763525
2014	3.701791415801145
2015	4.450622493967762