Year	Percent
1970	38.68313
1971	39.35743
1972	39.60784
1973	40.22989
1974	40.29851
1975	40.72727
1976	41.28114
1977	41.66667
1978	42.0339
1979	42.24422
1980	42.90323
1981	43.21767
1982	43.69231
1983	44.14414
1984	44.57478
1985	44.98567
1986	45.37815
1987	46.0274
1988	46.52406
1989	47.12042
1990	47.57033
1991	48.1203
1992	48.77451
1993	49.16067
1994	49.76526
1995	50.34483
1996	50.9009
1997	51.43488
1998	51.83585
1999	52.54237
2000	53.01455
2001	53.56415
2002	53.89222
2003	54.40313
2004	54.89443
2005	55.36723
2006	56.00739
2007	56.44283
2008	56.9395
2009	57.4171
2010	57.87671
2011	58.31933
2012	58.91089
2013	59.48136
2014	59.93641
2015	60.46875