Year	% of total
1970	82.53947838543955
1971	84.2590312831545
1972	84.23632640989092
1973	85.35770907556332
1974	84.40680826855922
1975	84.3226669899767
1976	83.6169975293724
1977	84.96823105900314
1978	83.11439796910204
1979	82.31711476358879
1980	81.5554752140949
1981	81.76057607340051
1982	80.72014887009875
1983	80.1765317982181
1984	80.28235474652074
1985	79.59211310378161
1986	78.4687335787728
1987	76.91359375054596
1988	76.96856900072149
1989	76.78203903455396
1990	80
1991	79.16903274654553
1992	78.74755745789523
1993	77.85153328347046
1994	77.37710965599926
1995	76.4792355751562
1996	75.14450867052022
1997	74.22833767199702
1998	72.94562647754137
1999	72.87527593818984
2000	72.34913989260035
2001	72.03947368421053
2002	72.66276388149726
2003	73.95754677405823
2004	74.04085700049826
2005	73.89538257481554
2006	74.24242424242425
2007	74.28363283147159
2008	73.94463950355188