Year	Percent
1972	20.38123
1973	20.44888
1974	20.19653
1975	20.40973
1976	19.06676
1986	26.25857
1987	29.08726
1988	27.41121
1989	30.51026
1990	28.51501
1991	24.49827
1992	27.5253
1993	24.70535
1994	27.87883
1995	30.15399
1996	27.61917
1997	24.8395
1999	23.43583
2000	26.69132
2001	26.41596
2005	33.617
2006	38.25157
2008	43.34755
2011	47.0037
2013	46.78784
2014	55.26713
2015	60.26677
2016	61.63699
2017	57.45436