Year	Percent
1974	2.01
1990	4.976
1991	11.496
1992	8.685
1993	7.765
1994	6.13
1995	5.818
1996	4.557
1997	5.272
1998	5.536
1999	6.285
2000	6.034
2001	5.824
2002	6.579
2003	7.274
2004	9.019
2005	7.309
2006	7.436
2007	6.023
2008	5.614
2009	6.616
2010	5.845
2011	5.046
2012	4.384
2013	3.657
2014	3.873
2015	3.398
2016	2.999
2017	3.026