Year	Percent
1979	12.98
1980	12.53
1981	11.42
1982	13.85
1983	18.3
1984	16.77
1985	15.15
1986	15.05
1987	14.93
1988	13.41
1989	11.15
1990	13.02
1991	17.49
1992	19.28
1993	18.54
1994	16.88
1995	15.2
1996	15.65
1997	15.85
1998	14.47
1999	13.12
2000	12.09
2001	13.48
2002	12.8
2003	11.97
2004	11.37
2005	10.62
2006	10.03
2007	9.37
2008	8.82
2009	11.46
2010	11.55
2011	11.38
2012	11.73
2013	12.22
2014	13.31
2015	13.11
2016	12.64
2017	12.59
2018	11.78
2019	11.74
2020	14.25