Year	Percent
1970	59.65517
1971	59.93266
1972	60.52632
1973	60.89744
1974	61.75549
1975	62.07951
1976	62.68657
1977	63.26531
1978	63.63636
1979	64.16667
1980	64.49864
1981	65.07937
1982	65.63307
1983	66.16162
1984	66.91358
1985	67.22892
1986	67.92453
1987	68.43318
1988	68.91892
1989	69.60352
1990	70.10753
1991	70.73684
1992	71.19342
1993	71.83099
1994	72.44094
1995	73.02505
1996	73.58491
1997	74.16974
1998	74.86438
1999	75.22124
2000	75.73657
2001	76.53061
2002	77
2003	77.45098
2004	77.92
2005	78.33595
2006	78.8906
2007	79.30514
2008	79.82196
2009	80.34934
2010	80.82976
2011	81.32022
2012	81.65517
2013	82.11382
2014	82.55659
2015	83.11518