Year	Percent
1975	10.55
1977	9.4
1980	9.1
1981	8.13
1982	11.46
1983	11.13
1984	13
1985	13.89
1986	12.94
1987	10.83
1991	10.12
1992	9.44
1993	7.8
1994	8.25
1995	8.72
1996	11.81
1997	12.14
1998	15
1999	20.06
2000	20.52
2001	15.04
2002	14.48
2003	13.22
2004	12.74
2005	11.06
2006	11.29
2007	10.25
2008	10.49
2009	11.29
2010	10.98
2011	10.11
2012	9.74
2013	9.05
2014	8.57
2015	8.3
2016	8.69
2017	8.87
2018	9.11
2019	9.96
2020	15.04