Year	Percent
1980	4.965
1981	4.63
1982	4.513
1983	4.438
1984	4.082
1985	4.207
1986	4.322
1987	3.499
1988	2.544
1989	2.677
1990	2.46
1991	2.081
1992	2.261
1993	2.68
1994	2.459
1995	1.942
1996	2.031
1997	2.46
1998	7.216
1999	6.686
2000	4.5344
2001	4.1723
2002	3.4555
2003	3.4403
2004	3.5737
2005	3.7251
2006	3.6349
2007	3.5628
2008	3.4701
2009	4.0837
2010	3.8226
2011	3.3721
2012	3.1871
2013	3.185
2014	3.323
2015	3.3351
2016	3.5736
2017	3.7047