Year	Percent
1978	3.8
1979	3.22
1980	3.19
1981	3.63
1982	5.32
1983	6.54
1984	6.16
1985	7.27
1986	6.75
1987	5.47
1988	4.81
1989	4.55
1990	5.04
1991	4.61
1992	4.8
1993	4.63
1994	4.71
1995	5.28
1996	6.96
1997	6.94
1998	7.23
1999	7.31
2000	7.33
2001	10.43
2002	11.86
2003	11.45
2004	10.82
2005	10.62
2006	10.25
2007	10.76
2008	11.82
2009	14.5
2010	13.07
2011	12.5
2012	12.57
2013	13.11
2014	12.64
2015	12.06
2016	12.11
2017	11.97
2018	11.42
2019	11.92
2020	11.64