Year	Percent
1970	75.83187
1971	76.32933
1972	76.80672
1973	77.26524
1974	77.86753
1975	78.28843
1976	78.84914
1977	79.54198
1978	79.94012
1979	80.4699
1980	81.09668
1981	81.5864
1982	82.05841
1983	82.65027
1984	83.08725
1985	83.64116
1986	84.17639
1987	84.69388
1988	85.31995
1989	85.69667
1990	86.28641
1991	86.73835
1992	87.29412
1993	87.83314
1994	88.35616
1995	88.86389
1996	89.24612
1997	89.82495
1998	90.28078
1999	90.73482
2000	91.16719
2001	91.59751
2002	92.11066
2003	92.51769
2004	92.91417
2005	93.30049
2006	93.67704
2007	94.13462
2008	94.49193
2009	94.84053
2010	95.18072
2011	95.42543
2012	95.75045
2013	96.15728
2014	96.46643
2015	96.76856