Year	Percent
1974	3.21
1976	3.3
1978	3.51
1979	2.81
1980	4.36
1981	4.59
1982	4.05
1983	3.94
1984	5.23
1985	5.34
1990	12.175
1991	14.307
1992	15.382
1993	12.772
1994	10.492
1995	8.89
1996	8.245
1997	9.66
1998	9.843
1999	10.212
2000	9.784
2001	10.739
2002	11.289
2003	12.207
2004	12.236
2005	10.33
2006	9.196
2007	8.43
2008	6.953
2009	8.636
2010	7.077
2011	6.328
2012	6.184
2013	5.817
2014	5.194
2015	4.873
2016	4.441
2017	3.847