Year	Percent
1970	50
1971	50.41322
1972	50.9434
1973	51.31579
1974	51.67095
1975	52.01005
1976	52.57985
1977	52.88462
1978	53.28638
1979	53.7931
1980	54.1573
1981	54.72527
1982	55.05376
1983	55.57895
1984	55.96708
1985	56.45161
1986	57.00197
1987	57.52896
1988	58.03403
1989	58.51852
1990	58.87681
1991	59.50266
1992	59.82609
1993	60.477
1994	60.93489
1995	61.3748
1996	61.95827
1997	62.51969
1998	63.06028
1999	63.58118
2000	63.9881
2001	64.52555
2002	65.1363
2003	65.6338
2004	66.11342
2005	66.71196
2006	67.28972
2007	67.62779
2008	68.29897
2009	68.82129
2010	69.24035
2011	69.85294
2012	70.36145
2013	70.93713
2014	71.52859
2015	71.98622