Year	Percent
1970	86.00583
1971	86.40227
1972	86.74033
1973	87.09677
1974	87.43455
1975	87.78626
1976	87.87129
1977	88.19277
1978	88.73239
1979	88.81279
1980	89.11111
1981	89.20086
1982	89.4958
1983	89.77505
1984	90.03984
1985	90.11628
1986	90.37736
1987	90.625
1988	90.69767
1989	90.76655
1990	91.0017
1991	90.90909
1992	91.12903
1993	91.19497
1994	91.39785
1995	91.74174
1996	92.04713
1997	92.34104
1998	92.62411
1999	93.03621
2000	93.43365
2001	93.8172
2002	94.18758
2003	94.54545
2004	95.01916
2005	95.23212
2006	95.67901
2007	95.99515
2008	96.41577
2009	96.70975
2010	96.99422
2011	97.38041
2012	97.75785
2013	98.01325
2014	98.36957
2015	98.60814