Year	Percent
1970	71.69518
1971	72.21374
1972	72.71364
1973	73.23529
1974	73.73737
1975	74.22096
1976	74.79109
1977	75.2394
1978	75.7047
1979	76.2533
1980	76.7834
1981	77.29592
1982	77.81955
1983	78.2984
1984	78.78788
1985	79.26103
1986	79.81221
1987	80.25404
1988	80.79545
1989	81.31991
1990	81.71806
1991	82.21258
1992	82.69231
1993	83.15789
1994	83.71369
1995	84.15133
1996	84.57661
1997	85.08946
1998	85.4902
1999	85.97679
2000	86.45038
2001	86.81733
2002	87.26766
2003	87.70642
2004	88.21396
2005	88.63026
2006	89.03625
2007	89.34498
2008	89.81002
2009	90.18771
2010	90.55649
2011	90.99249
2012	91.26134
2013	91.68026
2014	92.0904
2015	92.41214