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	99.8984771573604
1987	99.45496270797476
1988	99.17254060680355
1989	99.504806291873
1990	99.67014843320506
1991	99.78517722878625
1992	99.63817277250114
1993	99.51690821256038
1994	99.70449172576832
1995	99.66168091168092
1996	99.62033674480027
1997	99.68071519795659
1998	99.76278724981468
1999	99.75992091512498
2000	99.43050847457627
2001	99.3244138296463
2002	99.24987702902115
2003	99.37453089817363
2004	99.30857588937214
2005	99.32670395690906
2006	99.46043165467626
2007	99.43081301438352
2008	99.46524064171123
2009	99.51653587443946
2010	99.50598903701699
2011	99.54939578070595
2012	99.57821161725717
2013	99.62926490181313
2014	99.6377607025247
2015	99.03229199537184