Year	Percent
1970	72.07547
1971	72.69373
1972	73.02158
1973	73.33333
1974	73.9726
1975	74.58194
1976	74.8366
1977	75.15924
1978	76.01246
1979	76.29179
1980	76.8546
1981	77.3913
1982	77.90368
1983	78.39335
1984	78.86179
1985	79.36508
1986	80.05181
1987	80.50633
1988	80.94059
1989	81.35593
1990	81.99052
1991	82.17593
1992	82.76644
1993	83.14856
1994	83.91304
1995	84.25532
1996	84.79167
1997	85.10204
1998	85.42914
1999	86.10568
2000	86.39847
2001	87.03008
2002	87.29282
2003	87.72563
2004	88.31858
2005	88.71528
2006	89.11565
2007	89.48247
2008	90.01637
2009	90.36918
2010	90.70866
2011	91.19011
2012	91.65402
2013	92.10134
2014	92.39766
2015	92.81609