Year	Percent
1970	68.1431
1971	68.88519
1972	69.9187
1973	70.79365
1974	71.62791
1975	72.72727
1976	73.62963
1977	74.52967
1978	75.63739
1979	76.5928
1980	77.64228
1981	78.54305
1982	79.63684
1983	80.71066
1984	81.71642
1985	82.70402
1986	83.87097
1987	84.89461
1988	85.8783
1989	86.92221
1990	87.92913
1991	88.80435
1992	89.74359
1993	90.74658
1994	91.62358
1995	92.36253
1996	92.96482
1997	93.55159
1998	94.12341
1999	94.58414
2000	95.12894
2001	95.56604
2002	95.99254
2003	96.40884
2004	96.72429
2005	97.1223
2006	97.51111
2007	97.80316
2008	98.08862
2009	98.3677
2010	98.64061
2011	98.99075
2012	99.25125
2013	99.42387
2014	99.674
2015	99.91935