Year	Percent
1975	23.73
1976	23.24
1977	22.24
1978	23.65
1979	27.88
1980	27.87
1981	29.01
1982	28.4
1983	28.1
1984	27.24
1985	27.52
1986	29.42
1987	30.95
1991	30.09