Year	Percent
1970	52.35849
1971	52.88684
1972	53.0474
1973	53.64238
1974	53.99568
1975	54.33404
1976	54.75207
1977	55.26316
1978	55.64356
1979	56.20155
1980	56.54649
1981	57.0632
1982	57.5592
1983	58.03571
1984	58.39161
1985	59.00515
1986	59.4958
1987	59.96705
1988	60.42003
1989	60.85578
1990	61.3354
1991	61.89024
1992	62.33184
1993	62.84875
1994	63.40058
1995	63.79066
1996	64.30556
1997	64.80218
1998	65.41555
1999	65.87615
2000	66.36481
2001	66.92112
2002	67.45932
2003	68.01968
2004	68.523
2005	69.04762
2006	69.63658
2007	70.12687
2008	70.7151
2009	71.2528
2010	71.80617
2011	72.34273
2012	72.86325
2013	73.36842
2014	74.03946
2015	74.51382