Year	% of total
1971	83.19225260274104
1972	84.55158178772031
1973	85.2236436664464
1974	85.36731292707948
1975	86.33865578917208
1976	86.85619354872959
1977	87.4671089812951
1978	88.71850494547657
1979	88.90348749261162
1980	90.36044899994583
1981	90.40010193165509
1982	90.61288127599472
1983	90.08728290318928
1984	90.03597818365284
1985	90.0173930361971
1986	88.74772081577169
1987	88.44363078656973
1988	88.4135970502482
1989	88.52680143627893
1990	87.35333815881728
1991	87.40530592846062
1992	86.95013785564504
1993	86.97184566449263
1994	88.19844198685341
1995	86.18629766100923
1996	86.24386971719163
1997	86.65881761184077
1998	87.16154776036757
1999	87.09443948075406
2000	87.24953198622532
2001	88.27885621737491
2002	88.52239253374167
2003	88.87888767659304
2004	88.76018436433671
2005	88.63817567969086
2006	89.10735084924775
2007	88.90048469713261
2008	89.69529199444479
2009	90.57949072884934
2010	90.49508897459853
2011	90.4646096964222
2012	91.0569958148799
2013	90.57104538081045
2014	90.2784899713522
2015	90.4262079109407