Year	% of total
1971	34.82667810354455
1972	34.26583998634068
1973	34.27664575807538
1974	33.10911086894633
1975	33.714859635331386
1976	33.83613021215325
1977	33.72361430629126
1978	34.52456306077874
1979	33.905133490546255
1980	33.141790785190224
1981	32.69308152075878
1982	32.22168359699628
1983	31.899337655869402
1984	31.88540258141058
1985	31.856330888974327
1986	32.43972036216273
1987	32.9129020923534
1988	32.829937612840716
1989	32.94070552711486
1990	69.10946191695147
1991	68.91247736121706
1992	68.59733315591183
1993	67.66468125272333
1994	67.04395249042886
1995	66.81560022113408
1996	67.74201232909334
1997	67.66251591801169
1998	67.60378933547285
1999	67.98416731234941
2000	68.24623196156399
2001	68.08782152189193
2002	68.86604354983659
2003	70.55398787999111
2004	70.44062712229515
2005	71.03613097473276
2006	72.10308022810058
2007	72.7090564096731
2008	71.94430054883142
2009	71.53714923214328
2010	71.67511855605251
2011	72.91826137770109
2012	71.32354876288251
2013	71.3444544383659
2014	69.85325765071381
2015	68.87661401171937