Year	% of total
1970	88.61979756705206
1971	88.38201197022151
1972	88.51363379233193
1973	88.03310017093993
1974	87.13913783491309
1975	88.14656838619621
1976	87.61502309691296
1977	88.21170286712302
1978	88.50596379900998
1979	87.84113048744766
1980	87.1498405977801
1981	87.28710897560026
1982	87.307593770877
1983	86.43909883247052
1984	86.3435362124705
1985	86.57749356757591
1986	86.30684178938372
1987	86.44789809931514
1988	86.51283619025696
1989	86.07447238486905
1990	90.43824701195219
1991	89.03760356915232
1992	87.79472954230236
1993	88.53503184713377
1994	89.12529550827422
1995	89.23431203223949
1996	89.1389983117614
1997	89.02371759514617
1998	88.74862788144895
1999	88.50948509485094
2000	88.36461126005362
2001	88.1827731092437
2002	87.9854997410668
2003	87.73100616016427
2004	87.51902587519027
2005	87.36263736263736
2006	86.420395421436
2007	85.50646551724138
2008	85.11552928533047