Year	Percent
1975	6
1977	5.88
1979	6.16
1981	7.92
1983	11.85
1985	10.48
1987	9.9
1988	9.37
1989	8.7
1990	7.67
1991	7.28
1992	5.56
1993	6.29
1994	7.16
1995	7.16
1996	6.42
1997	5.51
1998	4.39
1999	3.62
2000	2.73
2001	2.12
2002	2.55
2003	3.59
2004	4.65
2005	5.87
2006	5
2007	4.15
2008	3.65
2009	4.35
2010	4.99
2011	4.98
2012	5.82
2013	7.24
2014	7.42
2015	6.87
2016	6.01
2017	4.84
2018	3.83
2019	3.38
2020	3.82