Year	Percent
1970	14.10019
1971	14.64182
1972	15.08658
1973	11.53989
1974	11.68699
1975	12.53343
1976	13.72777
1977	16.95928
1978	21.10463
1979	24.55284
1980	25.85563
1981	31.64242
1982	33.96778
1983	34.97333
1984	36.33908
1985	45.86744
1986	43.88169
1987	41.04569
1988	35.86132
1989	32.99697
1990	33.42222
1991	39.02545
1992	38.41687
1993	41.60007
1994	45.53133
1995	60.29451
1996	63.26415
1997	75.31001
1998	96.04648
1999	78.92073
2000	64.43094
2001	57.55173
2002	48.55872
2003	40.02078
2004	35.32196
2005	32.33256
2006	29.26893
2007	24.70719
2008	23.62508
2009	29.73241
2010	32.54369
2011	30.38157
2012	35.39178
2013	34.89111
2014	35.10632
2015	34.25171
2016	31.4314