Year	Percent
1978	1.67
1979	1.27
1980	1.24
1981	1.36
1982	2.14
1983	2.71
1984	2.44
1985	2.9
1986	2.66
1987	1.97
1988	1.69
1989	1.56
1990	1.66
1991	1.51
1992	1.52
1993	1.45
1994	1.56
1995	1.79
1996	2.6
1997	2.72
1998	2.69
1999	2.93
2000	2.98
2001	4.58
2002	5.17
2003	4.99
2004	4.43
2005	4.13
2006	3.91
2007	3.91
2008	4.15
2009	5.85
2010	5.21
2011	4.38
2012	4.24
2013	4.18
2014	3.96
2015	3.78
2016	3.91
2017	3.76
2018	3.71
2019	3.73
2020	3.84