Year	Percent
1975	15.2
1976	14.52
1977	13.97
1978	12.82
1979	11.38
1980	10.41
1981	10.08
1982	9.89
1983	9.49
1984	10.1
1985	9.9
1986	9.89
1987	9.6
1991	6.64