Year	Percent
1970	29.03226
1971	29.51289
1972	29.69188
1973	30.13699
1974	30.2139
1975	30.62827
1976	30.94629
1977	31.25
1978	31.54034
1979	32.05742
1980	32.24299
1981	32.72311
1982	32.88591
1983	33.26039
1984	33.61884
1985	33.96226
1986	34.49692
1987	34.73896
1988	35.23622
1989	35.64547
1990	36.03774
1991	36.41405
1992	36.77536
1993	37.30018
1994	37.73913
1995	38.05461
1996	38.62876
1997	39.01639
1998	39.54984
1999	40.06309
2000	40.55728
2001	41.03343
2002	41.57973
2003	42.0205
2004	42.52874
2005	43.0791
2006	43.55062
2007	44.14169
2008	44.57831
2009	45.13158
2010	45.66624
2011	46.12452
2012	46.625
2013	47.23247
2014	47.64208
2015	48.21429