Year	Percent
1978	1.57
1979	1.15
1980	1.11
1981	1.21
1982	2.08
1983	2.68
1984	2.44
1985	2.9
1986	2.75
1987	1.96
1988	1.7
1989	1.57
1990	1.68
1991	1.5
1992	1.47
1993	1.36
1994	1.51
1995	1.79
1996	2.72
1997	2.94
1998	2.93
1999	3.23
2000	3.36
2001	5.16
2002	5.91
2003	5.51
2004	4.83
2005	4.31
2006	4.05
2007	4.05
2008	4.39
2009	6.53
2010	5.8
2011	4.71
2012	4.49
2013	4.47
2014	4.27
2015	4.05
2016	4.19
2017	4