Year	Percent
1970	23.04833
1971	23.63636
1972	23.75887
1973	24.22145
1974	24.66216
1975	25
1976	25.40193
1977	25.70533
1978	26.38037
1979	26.94611
1980	27.19298
1981	27.63533
1982	28.1337
1983	28.80435
1984	29.52128
1985	29.87013
1986	30.45685
1987	31.26551
1988	31.96126
1989	32.46445
1990	33.33333
1991	33.93665
1992	34.73451
1993	35.71429
1994	36.44068
1995	37.26708
1996	38.13387
1997	38.88889
1998	39.61165
1999	40.30418
2000	40.96834
2001	41.7122
2002	42.32143
2003	43.00699
2004	43.73928
2005	44.20168
2006	44.81054
2007	45.55735
2008	46.11727
2009	46.6563
2010	47.2561
2011	47.90419
2012	48.45815
2013	48.91775
2014	49.57507
2015	50.06954