Year	Percent
1980	38.67
1981	38.81
1982	44.44
1983	43.45
1984	44.98
1985	45.8
1986	46.5
1987	46.84
1988	46.72
1989	45.94
1990	46.48
1991	43.7
1992	46.59
1993	46.88
1995	47.69
1996	48.4
1997	49.05
1998	49.43
1999	49.93
2000	49.45
2001	51.76
2002	53.09
2003	53.71
2004	55.32
2005	55.63
2006	55.11
2007	56.75
2008	57.36
2009	59.49
2010	58.05
2011	59.39
2012	58.72
2013	58.64
2014	59.74
2015	60
2016	61.14