Year	Percent
1973	3.15
1974	4.39
1976	4.61
1978	4.7
1979	3.69
1980	5.84
1981	6.28
1982	5.94
1983	5.24
1984	6.97
1985	7.02
1990	14.091
1991	16.421
1992	17.105
1993	14.866
1994	12.345
1995	10.743
1996	9.69
1997	10.904
1998	11.209
1999	11.541
2000	11.165
2001	12.013
2002	12.741
2003	13.811
2004	13.767
2005	11.633
2006	11.043
2007	9.812
2008	7.857
2009	9.181
2010	7.951
2011	6.951
2012	6.977
2013	6.237
2014	5.918
2015	5.392
2016	4.942
2017	4.32