Year	Percent
1978	6.93
1979	5.99
1980	5.35
1981	5.26
1982	5.3
1983	5.31
1984	5.04
1985	4.96
1986	5.02
1987	4.49
1988	4.1
1989	4.02
1990	3.85
1991	4.02
1992	3.94
1993	3.69
1994	3.79
1995	3.74
1996	3.5
1997	3.33
1998	3.19
1999	3.24
2000	3.14
2001	3.04
2002	3.08
2003	3.07
2004	3.01
2005	2.83
2006	2.67
2007	2.51
2008	2.58
2009	2.55
2010	2.47
2011	2.56
2012	2.58
2013	2.68
2014	2.72
2015	2.78
2016	2.81
2017	2.78