Year	Percent
1974	7.83
1976	10.15
1978	9.98
1979	8.33
1980	13.36
1981	13.81
1982	12.91
1983	12.75
1984	15.67
1985	17.77
1990	20.778
1991	20.077
1992	20.643
1993	18.87
1994	14.533
1995	12.852
1996	12.029
1997	13.86
1998	16.378
1999	15.898
2000	17.261
2001	18.705
2002	20.871
2003	22.123
2004	19.575
2005	17.07
2006	17.308
2007	15.315
2008	11.932
2009	15.54
2010	14.823
2011	11.921
2012	11.597
2013	10.43
2014	10.096
2015	8.925
2016	8.236
2017	6.738