Year	Percent
1973	22.65785
1974	23.15752
1976	30.21041
1977	32.96107
1978	34.41294
1979	35.61944
1980	38.24564
1981	41.94783
1983	39.84695
1984	38.62576
1985	35.09983
1986	34.29334
1987	34.87323
1988	34.32249
1989	33.43613
1990	31.3036
1991	32.83868
1992	30.80152
1993	31.93551
1994	32.78795
1995	31.60987
1996	32.64784
1997	30.60168
1998	32.05676
2000	33.53319
2001	39.23484
2006	33.81909
2007	37.14494
2009	38.51779
2011	48.14315
2012	47.59902
2013	47.92831
2014	49.60368
2015	55.98655
2016	60.01916