Year	Percent
1967	8.81634
1968	10.34489
1969	10.04717
1970	10.22765
1971	10.87231
1972	11.31008
1973	11.71181
1974	12.39414
1975	10.13043
1976	9.82783
1977	9.86387
1978	9.81251
1979	8.83002
1980	14.60883
1981	14.35146
1982	14.23549
1983	16.20444
1984	18.00717
1985	15.54061
1986	15.09456
1987	16.47722
1988	15.13285
1989	15.95331
1990	16.33473
1991	16.65678
1992	16.24004
1993	15.57613
1994	16.65826
1995	17.40243
1996	17.06286
1997	18.78689
1998	19.42961
1999	18.22635
2000	21.52095
2001	22.67034
2002	22.60111
2003	22.75921
2004	22.61041
2005	22.63186
2006	25.84892
2007	23.75802
2008	21.81469
2009	24.39085
2010	22.73405
2011	20.64908
2012	19.8672
2013	18.62334
2014	18.93199
2015	17.49729
2016	16.52554
2017	16.61698