Year	Percent
1970	55
1971	55.4007
1972	56.12245
1973	56.47841
1974	56.95793
1975	57.59494
1976	58.02469
1977	58.43373
1978	58.82353
1979	59.48276
1980	59.94398
1981	60.54795
1982	60.96257
1983	61.6188
1984	61.9898
1985	62.59352
1986	63.01703
1987	63.80952
1988	64.4186
1989	64.77273
1990	65.55556
1991	66.08696
1992	66.80851
1993	67.35967
1994	67.88618
1995	68.58847
1996	69.2607
1997	70.09524
1998	70.57728
1999	71.2204
2000	71.83601
2001	72.60035
2002	73.16239
2003	73.86935
2004	74.38424
2005	74.91961
2006	75.55205
2007	76.19784
2008	76.66667
2009	77.26597
2010	77.81022
2011	78.36676
2012	78.90295
2013	79.41989
2014	79.8103
2015	80.29294