Year	Percent
1970	33.47529
1971	34.59367
1972	35.11583
1973	32.92709
1974	28.86324
1975	30.79907
1976	27.50014
1977	27.29249
1978	23.05459
1979	21.89921
1980	21.49977
1981	24.82864
1982	27.8438
1983	31.16532
1984	33.4302
1985	43.62469
1986	46.41564
1987	49.69883
1988	45.73618
1989	45.50728
1990	45.56831
1991	44.08147
1992	36.96312
1993	35.42057
1994	27.53585
1995	27.71854
1996	30.55202
1997	30.81805
1998	34.42506
1999	41.07106
2000	35.06844
2001	38.18024
2002	35.18771
2003	40.75744
2004	33.79364
2005	26.51475
2006	24.41734
2007	22.01922
2008	19.91507
2009	23.65433
2010	23.23991
2011	23.07143
2012	21.64965
2013	24.51573
2014	27.71077
2015	38.7697
2016	43.33643