Year	Percent
1971	11.52
1972	11.83
1973	11.61
1974	13.13
1976	19.65
1977	19.04
1978	16.73
1979	14.53
1980	17.1
1981	17.83
1982	19.91
1983	22.24
1984	20
1985	20.67
1986	19.53
1987	17.01
1988	15.01
1989	14.6
1990	14.52
1991	16.18
1992	16.93
1993	16.91
1994	14.6
1995	13.93
1996	13.64
1997	13.8
1998	13.46
1999	11.81
2000	10.08
2001	11.4
2002	11.94
2003	11.78
2004	10.31
2005	11.35
2006	11.01
2007	10.93
2008	11.48
2009	15
2010	16.1
2011	15.7
2012	14.5
2013	14.3
2014	13.9
2015	12
2016	11.8
2017	10.8
2018	9.2
2019	8.3