Year	Percent
1979	11.89
1980	9.02
1981	10.1
1982	9.89
1984	9.79
1986	9.48
1987	8.92
1988	7.85
1989	8.42
1990	8.88
1991	14.95
1992	24.48
1993	30.79
1994	31.16
1995	41.19
1996	41.56
1997	35.43
1998	34.64
1999	28.59
2000	28.35
2001	26.6
2002	28.22
2003	27.81
2004	27.53
2005	20.08
2006	18.73
2007	16.51
2008	16.45
2009	21.51
2010	21.4
2011	20.06
2012	18.96
2013	19.92
2014	20.55
2015	22.45
2016	20.15
2017	20.13
2018	17.03
2019	17.2
2020	21.36