Year	Percent
1974	7.8
1976	9.83
1978	9.87
1979	8.04
1980	13.25
1981	14.33
1982	14.06
1983	12.83
1984	16.25
1985	17.31
1990	21.81
1991	22.11
1992	22.64
1993	20.69
1994	16.66
1995	14.93
1996	13.55
1997	15.03
1998	16.94
1999	16.71
2000	17.3
2001	18.68
2002	20.82
2003	22.39
2004	20.64
2005	17.85
2006	18.38
2007	16.22
2008	12.46
2009	14.71
2010	14.22
2011	11.83
2012	12.14
2013	10.54
2014	10.59
2015	9.3
2016	8.63
2017	7.26
2018	7.15
2019	6.68
2020	7.92