Year	Percent
1970	81.19266
1971	81.61435
1972	82.01754
1973	82.40343
1974	82.77311
1975	83.33333
1976	83.87097
1977	84.22091
1978	84.91296
1979	85.22727
1980	85.71429
1981	86.18182
1982	86.63102
1983	87.08551
1984	87.5
1985	87.91946
1986	88.46787
1987	88.85299
1988	89.38193
1989	89.73561
1990	90.22901
1991	90.70465
1992	91.02941
1993	91.47399
1994	91.91489
1995	92.46862
1996	92.86694
1997	93.12668
1998	93.63395
1999	94.00261
2000	94.4801
2001	94.82323
2002	95.2795
2003	95.59902
2004	96.02888
2005	96.4455
2006	96.7366
2007	97.12974
2008	97.51131
2009	97.77283
2010	98.24369
2011	98.48649
2012	98.9339
2013	99.15966
2014	99.4824
2015	99.89785