Year	Percent
1970	75.87822
1971	76.48402
1972	77.06013
1973	77.82609
1974	78.17797
1975	78.92562
1976	79.43548
1977	80.11811
1978	80.96154
1979	81.42589
1980	82.05128
1981	82.82648
1982	83.42059
1983	83.98637
1984	84.69218
1985	85.36585
1986	86.16852
1987	86.80124
1988	87.40516
1989	87.9822
1990	88.67925
1991	89.34659
1992	90.12517
1993	90.73569
1994	91.33333
1995	91.89542
1996	92.54499
1997	93.05556
1998	93.42432
1999	93.90244
2000	94.47779
2001	94.92326
2002	95.2381
2003	95.65714
2004	96.17117
2005	96.56319
2006	96.83406
2007	97.2043
2008	97.66702
2009	97.91014
2010	98.24923
2011	98.57868
2012	98.8978
2013	99.20949
2014	99.4152
2015	99.71126