Year	Percent
1978	9.45
1979	9.59
1980	9.75
1981	9.94
1982	10.15
1983	10.35
1984	10.51
1985	10.65
1986	10.82
1987	11.07
1988	11.06
1989	10.96
1990	9.24
1992	9
1993	9.61
1994	9.79
1997	11.71
1998	12.04
2015	16.7
2017	15.94