Year	Percent
1978	1.86
1979	1.53
1980	1.47
1981	1.65
1982	2.25
1983	2.76
1984	2.46
1985	2.92
1986	2.53
1987	1.97
1988	1.68
1989	1.56
1990	1.64
1991	1.53
1992	1.57
1993	1.59
1994	1.65
1995	1.8
1996	2.42
1997	2.37
1998	2.33
1999	2.46
2000	2.44
2001	3.71
2002	4.1
2003	4.25
2004	3.89
2005	3.88
2006	3.71
2007	3.72
2008	3.83
2009	4.96
2010	4.45
2011	3.96
2012	3.92
2013	3.8
2014	3.56
2015	3.44
2016	3.57
2017	3.45