Year	Percent
1970	33.58907
1971	35.25412
1972	43.49486
1973	70.26878
1974	56.62906
1975	50.31171
1976	50.13577
1977	47.84307
1978	43.3902
1979	41.84607
1980	38.79189
1981	34.81346
1982	35.32885
1983	37.82561
1984	35.86942
1985	39.98836
1986	45.6076
1987	47.35625
1988	42.52459
1989	44.07176
1990	49.51057
1991	50.22129
1992	50.70682
1993	47.32934
1994	52.63141
1995	49.48034
1996	47.27608
1997	48.56421
1998	52.38566
1999	54.69304
2000	45.21922
2001	44.71483
2002	46.50767
2003	42.481
2004	36.28085
2005	30.43634
2006	26.59714
2007	27.10322
2008	28.55732
2009	32.6486
2010	34.10066
2011	28.88742
2012	26.30198
2013	23.79832
2014	23.6794
2015	22.86724
2016	24.10641