Year	Percent
1970	35.48387
1971	35.78947
1972	36.73469
1973	36.63366
1974	36.53846
1975	37.73585
1976	37.61468
1977	37.5
1978	38.26087
1979	38.65546
1980	38.52459
1981	39.2
1982	39.53488
1983	40.15152
1984	39.70588
1985	40
1986	41.25874
1987	41.4966
1988	41.72185
1989	41.93548
1990	42.5
1991	42.68293
1992	43.19527
1993	43.93064
1994	43.82022
1995	44.2623
1996	44.91979
1997	45.3125
1998	45.68528
1999	46.0396
2000	46.37681
2001	46.47887
2002	47.24771
2003	47.32143
2004	47.59825
2005	48.08511
2006	48.54772
2007	48.98785
2008	49.40711
2009	49.61538
2010	50
2011	50.18315
2012	50.89606
2013	51.04895
2014	51.53584
2015	52