Year	Percent
1970	48.3871
1971	49.02913
1972	49.64539
1973	50.11547
1974	50.79007
1975	51.54185
1976	52.04301
1977	52.94118
1978	53.48361
1979	54.30862
1980	54.99022
1981	55.83174
1982	56.52985
1983	57.48175
1984	58.28877
1985	59.23345
1986	60.20408
1987	61.23128
1988	62.11382
1989	63.11606
1990	64.23017
1991	65.34954
1992	66.56761
1993	67.73256
1994	68.99004
1995	70.33426
1996	71.31148
1997	72.34899
1998	73.12253
1999	74.09326
2000	74.90446
2001	75.71965
2002	76.60099
2003	77.23971
2004	78.06913
2005	78.78077
2006	79.35409
2007	80.11364
2008	80.76063
2009	81.27753
2010	81.8872
2011	82.56684
2012	83.03477
2013	83.59294
2014	84.13511
2015	84.66196