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	100
1991	100
1992	100
1993	100
1994	100
1995	100
1996	100
1997	100
1998	100
1999	100
2000	100
2001	100
2002	100
2003	100
2004	100
2005	99.97715330134795
2006	99.97850386930352
2007	99.93841100390064
2008	99.70466627288836
2009	99.40556088207096
2010	98.62833521232619
2011	96.3887198214648
2012	94.55162179351284
2013	92.37762237762239
2014	92.71264367816092
2015	91.21994264284139