Year	Percent
1970	59.04437
1971	59.46844
1972	59.87055
1973	60.56782
1974	60.7362
1975	61.37725
1976	61.80758
1977	62.21591
1978	62.70718
1979	63.07278
1980	63.51706
1981	64.19437
1982	64.42786
1983	65.04854
1984	65.48463
1985	66.12903
1986	66.74157
1987	67.17724
1988	67.80384
1989	68.39917
1990	68.96552
1991	69.56522
1992	70.27027
1993	70.86466
1994	71.55963
1995	72.27191
1996	73.02977
1997	73.75643
1998	74.32886
1999	74.87685
2000	75.52335
2001	76.18297
2002	76.81607
2003	77.42424
2004	78.00892
2005	78.57143
2006	79.11302
2007	79.77528
2008	80.16529
2009	80.78484
2010	81.38298
2011	81.85379
2012	82.54172
2013	82.97604
2014	83.62283
2015	84.14634