Year	Percent
1978	23.05
1979	23.18
1980	23.14
1981	23.21
1982	23.1
1983	23.38
1984	23.34
1985	23.29
1986	23.32
1987	23.62
1988	23.91
1989	23.86
1990	21.03
1992	21.95
1993	21.49
1994	21.53
1997	24.93
1998	25.15
2015	31.41
2017	33.47