Year	Percent
1970	5.41
1971	5.29
1972	5.45
1973	5.05
1974	4.98
1975	5.05
1976	4.8923
1977	4.5991
1978	3.7282
1979	4.6546
1980	6.197
1981	5.735
1982	5.493
1983	5.213
1984	4.765
1985	4.991
1986	4.919
1987	3.916
1988	3.024
1989	3.064
1990	2.91
1991	2.686
1992	2.763
1993	3.291
1994	2.842
1995	2.316
1996	2.364
1997	2.818
1998	7.828
1999	7.189
2000	5
2001	4.5
2002	3.7
2003	3.8
2004	3.9
2005	4
2006	3.8
2007	3.7
2008	3.6
2009	4.1
2010	4
2011	3.6
2012	3.4
2013	3.3
2014	3.6
2015	3.7
2016	3.8
2017	3.8