Year	Percent
1970	43.49776
1971	43.66812
1972	43.82979
1973	44.39834
1974	44.53441
1975	45.05929
1976	45.38462
1977	45.69288
1978	46.15385
1979	46.42857
1980	46.6899
1981	47.11864
1982	47.35099
1983	47.74194
1984	48.26498
1985	48.61538
1986	48.94895
1987	49.12281
1988	49.71429
1989	50.13928
1990	50.40872
1991	50.79787
1992	51.29534
1993	51.64557
1994	52.09877
1995	52.657
1996	53.06604
1997	53.33333
1998	53.93258
1999	54.28571
2000	54.72103
2001	55.13627
2002	55.64682
2003	56.2249
2004	56.58153
2005	57.11538
2006	57.5188
2007	58.01105
2008	58.48375
2009	59.0106
2010	59.34256
2011	59.93209
2012	60.39933
2013	61.01142
2014	61.44
2015	61.91223