Year	% of total
1971	63.543905601880695
1972	65.04733942179612
1973	66.99667849155651
1974	67.43125117906223
1975	67.77183773218843
1976	68.86187055685753
1977	69.45825615070076
1978	70.3851600083501
1979	70.67195853374588
1980	71.20532527422333
1981	70.95383169596988
1982	70.93398095395183
1983	69.11760281794925
1984	67.97178358784753
1985	67.85613826316222
1986	68.143036918765
1987	68.09186343816567
1988	68.57675676778499
1989	68.54370462987627
1990	68.61811674729762
1991	69.25649184262423
1992	69.70537905367878
1993	69.98512081530264
1994	70.31219854673223
1995	70.24147821283933
1996	70.79158895788296
1997	71.44607608339693
1998	72.1744548222936
1999	72.07697935954138
2000	72.68078344673764
2001	72.9200848235522
2002	72.11837078949685
2003	71.54249837842697
2004	71.66790986009751
2005	71.71577622164509
2006	71.53938668114901
2007	70.85605913661284
2008	71.07303107620722
2009	70.92385671214352
2010	70.74873182229068
2011	71.30043371115983
2012	72.27252951910725
2013	72.59932165707602
2014	72.7642902239619
2015	90.4262079109407