Year	Percent
1977	2.85
1978	3.4
1979	4.08
1980	5.08
1981	6.2
1982	6.99
1983	7.4
1984	9.93
1985	10.49
1986	11.38
1987	9.48
1988	9.04
1989	9.14
1990	8.22
1991	8.15
1992	9.12
1993	10.78
1994	12.76
1995	12.31
1996	11.58
1997	11.5
1998	10.26
1999	9.63
2000	9.82
2001	6.34
2002	7.07
2003	6.82
2004	7.47
2005	6.3
2006	5.76
2007	5.97
2008	7.36
2009	12.07
2010	14.21
2011	15.1
2012	18.02
2013	20.02
2014	19.97
2015	18.6
2016	17.03
2017	15.32
2018	13.77
2019	12.64
2020	12.5