Year	Percent
1981	20.51
1983	21.28
1985	29.82
1986	32.62
1987	40.07
1988	39.37
1989	39.82
1990	36.4
1991	34.16
1993	33.49
1995	31.01
1996	28.49
1998	26.95
1999	25.36
2000	23.18
2002	21.11
2005	16.48
2006	12.98
2007	11.32
2008	10.47
2009	11.74
2010	9.89
2011	8.7
2012	8.69
2013	6.32
2014	5.88
2015	5.86
2016	8.71