Year	Percent
1979	32.52
1980	32.94
1981	33.08
1982	33.3
1983	33.46
1984	33.74
1985	34
1986	34.2
1987	34.48
1988	35.04
1989	36.01
1990	37.32
1991	39.34
1992	40.25
1993	41.3
1994	42.01
1995	42.65
1996	43.06
1997	42.65
1998	43.19
1999	45.37
2000	53.68
2001	57.46
2002	56.57
2003	56.69
2004	56.23
2005	56.78
2006	57.42
2007	56.96
2008	56.1
2009	57.67
2010	60.21
2011	61.77
2012	62.24
2013	63.15
2014	62.88
2015	63.25
2016	63.46
2017	63.09