Year	Percent
1981	3.42
1982	4.94
1983	7.81
1984	8.1
1985	7.8
1986	7.36
1987	7.36
1988	7.65
1989	7.46
1990	7.02
1991	7.66
1992	7.84
1993	8.61
1994	8.86
1995	9.06
1996	9.66
1997	9.58
1998	10.84
1999	11.85
2000	11.25
2001	10.46
2002	9.97
2003	9.41
2004	10.31
2005	9.99
2006	9.01
2007	8.4
2008	7.76
2009	9.62
2010	12.71
2011	17.86
2012	24.44
2013	27.47
2014	26.49
2015	24.9
2016	23.54
2017	21.49
2018	19.29
2019	17.31
2020	16.3