Year	Percent
1960	22.06897
1961	23.86364
1962	19.58763
1963	17.16738
1964	14.32836
1965	13.6612
1966	16.51282
1967	18.78354
1968	13.85656
1969	14.94669
1970	3.39623
1971	17.73916
1972	17.15712
1973	34.1083
1974	15.85344
1975	18.89774
1976	20.95898
1977	21.48539
1978	22.71023
1979	24.0415
1980	17.34632
1981	21.39046
1982	19.79652
1983	14.25354
1984	12.1267
1985	11.37877
1986	11.18166
1987	14.29512
1988	14.66975
1989	12.06646
1990	12.20085
1991	15.12534
1992	15.3849
1993	15.6413
1994	15.87163
1995	15.40771
1996	15.24021
1997	16.84529
1998	17.33758
1999	15.07533
2000	14.45702
2001	14.32794
2002	13.07291
2003	15.20631
2004	17.46846
2005	17.69886
2006	19.46057
2007	19.52606
2008	23.20809
2009	19.62477
2010	19.40761
2011	20.88231
2012	22.91538
2013	22.48441
2014	21.20281
2015	19.70539
2016	17.79839
2017	15.71596