Year	Percent
1971	0.43889
1972	0.62734
1976	0.53172
1978	0.4619
1979	0.43708
1980	0.43638
1981	0.44442
1982	0.43888
1983	0.4567
1984	0.4665
1985	0.48359
1987	0.52556
1988	0.52636
1989	0.54803
2000	0.64891