Year	Percent
1970	51.26354
1971	51.40845
1972	51.89003
1973	52.34899
1974	52.78689
1975	53.20513
1976	53.4375
1977	53.82263
1978	54.32836
1979	54.8105
1980	55.27066
1981	55.71031
1982	56.13079
1983	56.38298
1984	56.88312
1985	57.50636
1986	57.9602
1987	58.39416
1988	58.66983
1989	59.30233
1990	59.90888
1991	60.35635
1992	60.78431
1993	61.19403
1994	61.79541
1995	62.37219
1996	62.8
1997	63.52941
1998	63.91555
1999	64.47368
2000	65.00921
2001	65.70397
2002	66.19469
2003	66.72444
2004	67.34694
2005	67.83333
2006	68.46405
2007	68.91026
2008	69.49686
2009	70.06173
2010	70.49924
2011	71.17385
2012	71.72012
2013	72.2063
2014	72.85513
2015	73.34254