Year	% of total
1971	67.97081924402617
1972	68.28538526620834
1973	69.97026739507396
1974	70.46069273147789
1975	70.52809927192288
1976	71.41666687404748
1977	71.9530417620628
1978	73.12634078398408
1979	73.04884095813368
1980	73.63076938102262
1981	73.56061642318782
1982	73.35550700582411
1983	71.89404632744005
1984	70.89654901558089
1985	70.38940480361092
1986	70.64157416252279
1987	70.35065218014262
1988	70.74417252013532
1989	70.84407394858552
1990	70.75953404632337
1991	71.29772811025427
1992	71.88772811723038
1993	71.93402608048892
1994	72.49866497719178
1995	72.25884465750158
1996	72.9294135159567
1997	73.40695998690863
1998	74.2048175419698
1999	74.0941305995057
2000	74.49533258131547
2001	74.78302219257267
2002	74.30389892275673
2003	73.68151213433907
2004	73.64484458581873
2005	73.58924734510613
2006	73.64012248753716
2007	72.94927443786403
2008	73.34611014174233
2009	73.18633369616491
2010	73.49142096457471
2011	73.64050076483645
2012	74.28230334072447
2013	74.27159892561902
2014	73.34633717730591
2015	87.88038849631673