Year	Percent
1983	33.53
1984	33.55
1985	33.65
1986	33.68
1987	33.22
1988	34
1989	35.45
1990	31.09
1991	32.2
1992	31.09
1993	33.98
1994	35.38
1995	35.78
1996	37.71
1997	42.32
1998	46.58
1999	46.51
2000	48.11
2001	49.22
2002	48.29
2003	48.9
2004	48.56
2005	48.61
2006	48.1
2007	48.83
2008	48.28
2009	49.21
2010	48.05
2011	48.04
2012	48.06
2013	48.52
2014	48.94
2015	49.58
2016	49.34
2017	49.28