Year	Percent
1970	10.339
1971	11.27711
1972	11.38615
1973	11.11053
1974	10.44978
1975	11.08601
1976	10.77164
1977	13.65426
1978	15.03202
1979	16.54122
1980	16.20887
1981	16.06292
1982	19.2308
1983	21.54712
1984	26.83761
1985	29.18281
1986	41.54555
1987	41.87451
1988	35.32664
1989	32.8172
1990	38.8443
1991	30.82846
1992	27.32862
1993	26.07905
1994	24.62621
1995	23.00994
1996	22.10478
1997	20.01706
1998	19.18389
1999	21.37765
2000	20.71008
2001	23.51469
2002	22.08202
2003	23.86176
2004	34.36338
2005	35.56919
2006	37.04182
2007	38.10649
2008	36.37157
2009	40.50469
2010	37.52
2011	35.39965
2012	30.81543
2013	32.79464
2014	33.81757
2015	32.54982
2016	31.65668