Year	Percent
1971	0.42626
1972	0.424
1973	0.43411
1974	0.44901
1975	0.483
1976	0.5024
1977	0.54849
1978	0.58038
1979	0.69679
1980	0.73724
1981	0.77534
1982	0.78926
1983	0.79329
1984	0.77891
1985	0.76456
1986	0.75906
1987	0.76804
1988	0.7908
1989	0.77414
1993	0.78788
1996	0.79054
1999	0.7797
2000	0.77225
2003	0.81188
2004	0.79053
2007	0.81409