Year	Percent
1970	58.1864
1971	58.867
1972	59.375
1973	60.0939
1974	60.77982
1975	61.43498
1976	62.0614
1977	62.7409
1978	63.38912
1979	64.13934
1980	64.92986
1981	65.68627
1982	66.28352
1983	67.16698
1984	68.01471
1985	68.70504
1986	69.3662
1987	70.1209
1988	70.89679
1989	71.64179
1990	72.47557
1991	73.32268
1992	73.98119
1993	74.76923
1994	75.49168
1995	76.22585
1996	76.75439
1997	77.26619
1998	77.76204
1999	78.38215
2000	78.738
2001	79.18919
2002	79.65426
2003	80.07864
2004	80.51613
2005	80.94028
2006	81.35169
2007	81.75092
2008	82.13852
2009	82.63473
2010	83.11688
2011	83.37209
2012	83.94495
2013	84.29379
2014	84.63252
2015	85.07135