Year	Percent
1976	49.60392
1977	50.52802
1978	50.52672
1979	51.68575
1980	51.59591
1981	52.20078
1982	53.44495
1983	54.00409
1984	54.22134
1985	54.58825
1986	55.03607
1987	55.58786
1988	55.73285
1989	56.06705
1990	56.10866
1991	56.4493
1992	57.34876
1993	58.39536
1994	58.1748
1995	58.91782
1996	58.68089
1997	58.4916
1998	58.86279
1999	58.73122
2000	59.30902
2001	59.48753
2002	60.2957
2003	60.39357
2004	60.31827
2005	60.57243
2006	60.70338
2007	60.31531
2008	61.02663
2009	62.16858
2010	62.29416
2011	62.27624
2012	62.00086
2013	62.32658
2014	62.65311
2015	63.06258
2016	63.26051
2017	62.79439