Year	Percent
1971	31.02459
1972	31.17826
1973	28.45672
1974	24.49567
1975	30.01319
1976	28.95747
1977	30.37906
1978	24.65854
1979	8.90715
1980	3.90221
1981	3.62275
1982	1.2491
1983	1.16836
1984	0.46436
1985	0.53602
1986	1.12881
1987	0.82656
1988	1.11154
1989	1.07027