Year	Percent
1970	2.9
1971	3.29
1972	2.56
1973	2.33
1974	2.7
1975	2.63
1976	1.9827
1977	2.4327
1978	2.2429
1979	2.4323
1980	3.529
1981	2.445
1982	2.549
1983	2.236
1984	2.208
1985	2.359
1986	2.08
1987	1.841
1988	1.756
1989	1.84
1990	1.785
1991	1.992
1992	2.139
1993	2.259
1994	1.932
1995	1.688
1996	1.586
1997	2.305
1998	5.667
1999	5.099
2000	3.6
2001	3.3
2002	2.8
2003	3.3
2004	3.4
2005	3.4
2006	2.9
2007	2.6
2008	2.6
2009	3
2010	3.3
2011	3.1
2012	3
2013	2.9
2014	3.5
2015	3.6
2016	3.6
2017	3.6