Year	Percent
1970	13.04844
1971	15.37698
1972	11.58998
1973	17.93959
1974	19.53588
1975	17.64539
1976	20.21998
1977	28.32207
1978	30.55471
1979	38.21838
1980	33.86241
1981	42.17847
1982	60.09597
1983	73.78968
1984	74.65264
1985	88.13596
1986	79.27734
1987	81.13752
1988	73.34663
1989	73.09113
1990	58.28829
1991	58.7906
1992	73.33917
1993	56.85705
1994	88.42967
1995	65.70672
1996	59.50671
1997	63.04962
1998	58.72656
1999	55.59362
2000	54.74123
2001	55.15817
2002	53.15042
2003	38.42431
2004	35.96466
2005	32.42294
2006	12.68278
2007	14.91766
2008	13.68157
2009	18.64568
2010	23.12014
2011	23.96025
2012	25.47196
2013	22.1574
2014	21.2504
2015	26.4977
2016	27.05924