Year	Percent
1960	6.69555
1961	6.9088
1962	9.87661
1963	12.31646
1964	10.79939
1965	7.97006
1966	7.84211
1967	8.66828
1968	9.71583
1969	6.22264
1970	9.84969
1971	7.77846
1972	11.06928
1973	14.93726
1974	15.05518
1975	14.31417
1976	14.20971
1977	19.68237
1978	22.99356
1979	25.83281
1980	28.11321
1981	20.29158
1982	20.58824
1983	12.54548
1984	3.148
1985	12.74722
1986	11.60146
1987	11.65251
1988	19.05182
1989	13.67755
1990	11.01569
1991	7.47631
1992	6.92574
1993	6.4014
1994	10.3929
1995	7.317
1996	9.65414
1997	10.85953
1998	11.26092
1999	10.22051
2000	11.43424
2001	12.12018
2002	14.18118
2003	15.78583
2004	13.8479
2005	22.84795
2006	23.58362
2007	22.89897
2008	32.09172
2009	34.73832
2010	39.95157
2011	38.39456
2012	36.17814
2013	36.15066
2014	37.4298
2015	40.04767
2016	33.86361
2017	33.69306