Year	Percent
1970	62.07729
1971	62.5
1972	63.0485
1973	63.43115
1974	64.01766
1975	64.36285
1976	64.90486
1977	65.42443
1978	65.9919
1979	66.33663
1980	66.99029
1981	67.49049
1982	67.84387
1983	68.48816
1984	69.10714
1985	69.58042
1986	70.03425
1987	70.4698
1988	71.05263
1989	71.6129
1990	72.1519
1991	72.55814
1992	73.21157
1993	73.73134
1994	74.23133
1995	74.71264
1996	75.42373
1997	75.86685
1998	76.43052
1999	76.87166
2000	77.39816
2001	77.90698
2002	78.52605
2003	78.90137
2004	79.48403
2005	79.95169
2006	80.4038
2007	80.84112
2008	81.47296
2009	81.87995
2010	82.38573
2011	82.87596
2012	83.35135
2013	83.81257
2014	84.26023
2015	84.69493