Year	% of total
1971	100
1972	100
1973	100
1974	100
1975	100
1976	100
1977	100
1978	100
1979	100
1980	100
1981	100
1982	100
1983	100
1984	100
1985	100
1986	100
1987	100
1988	100
1989	100
1990	73.4481562825107
1991	73.40395346637662
1992	70.34432412702274
1993	69.06085237258348
1994	68.5302697983433
1995	68.4228277088486
1996	67.67312142729988
1997	69.4056496754877
1998	68.3004283608002
1999	71.80271394362056
2000	73.71524118201773
2001	81.10538403417294
2002	83.69080544110177
2003	86.73790849673203
2004	86.9979671618452
2005	86.5736640094479
2006	85.61129666986342
2007	85.67244863148503
2008	84.13858961802154
2009	72.56981232898167
2010	70.21164924791829
2011	69.79050452460642
2012	72.37374852767962
2013	76.7028030012288
2014	75.0636613791909
2015	76.21003972382483