Year	Percent
1970	43.82022
1971	44.2623
1972	44.38503
1973	44.79167
1974	45.17766
1975	45.54455
1976	45.89372
1977	46.00939
1978	46.78899
1979	46.875
1980	46.95652
1981	47.65957
1982	48.13278
1983	48.17814
1984	48.4252
1985	48.84615
1986	49.06367
1987	49.45055
1988	50
1989	50.17422
1990	50.68027
1991	50.66225
1992	51.13269
1993	51.41956
1994	51.85185
1995	52.10843
1996	51.90616
1997	52.149
1998	52.23464
1999	52.45902
2000	52.8
2001	52.86458
2002	53.18066
2003	53.34988
2004	53.64078
2005	53.79147
2006	54.16667
2007	54.29864
2008	54.64602
2009	54.97835
2010	55.29661
2011	55.48654
2012	55.98377
2013	56.15079
2014	56.50485
2015	56.84411