Year	% of total
1971	75.2330386950626
1972	74.74973149958704
1973	74.27176804129148
1974	76.92359826869304
1975	77.62223035934447
1976	79.34049905000516
1977	79.56475889419077
1978	83.70193080142904
1979	85.81948122886155
1980	85.50880583526101
1981	86.04535007309333
1982	86.07015893786337
1983	87.77386888862249
1984	87.02189064173544
1985	86.78251050991716
1986	87.93423509830087
1987	87.5322956586706
1988	87.62776346605227
1989	88.83480461043335
1990	89.91071803977057
1991	91.6818575571192
1992	92.45778839044377
1993	92.85170483005473
1994	92.3740724076614
1995	93.04961025505854
1996	93.94502111324978
1997	95.04526802952364
1998	94.59444279395575
1999	94.1380283359755
2000	94.97309691349739
2001	95.17806382639537
2002	95.62841972689418
2003	95.99111004184125
2004	96.21646697003821
2005	96.82708397574073
2006	96.69407554690258
2007	96.94482832521211
2008	96.76022577083843
2009	96.66434839479231
2010	96.89621303251099
2011	96.81165029369001
2012	96.74023319379408
2013	96.7518810939698
2014	96.62819889780808